In the culmination of some two months of discussions that have blurred the lines between labor-management dialogue and plain old show-business ballyhoo, NBC’s “The Tonight Show With Jay Leno” and “Late Night With Conan O’Brien” returned to the airwaves Wednesday night — minus the contribution of their respective writing staffs, which remain on strike with the Writers Guild of America.

For anyone who has forgotten what classic, late-night television once looked and sounded like, John Landis’s recent documentary portrait of Don Rickles, “Mr. Warmth,” which featured vintage clips of “The Tonight Show Starring Johnny Carson,” offered an inadvertent reminder of just how bland NBC’s late-night flagship has grown since Mr. Leno took it over from Carson in 1992. Built on slow-pitch, call-and-response comedy, Mr. Leno’s “Tonight Show” is the television equivalent of Kraft macaroni and cheese — consistent, bland, brightly colored, and easy to chew and to swallow, so long as one doesn’t dwell on what it’s made of.

Forced to write his own jokes (Mr. Leno has been a credited member of the “Tonight Show” writing staff for most of his tenure behind the desk) and to work with a crew that has been on an eight-week hiatus, Mr. Leno offered, if nothing else, a discernibly from-scratch taste that has long been absent from NBC’s Burbank studio. Mr. Leno’s ingratiating audience handclasps and shrugging half-smirk have more or less rendered him a human lava lamp for the sweatpants-and-popcorn set. On Wednesday, however, the host actually achieved some flashes of incandescence. His monologue, typically a toothless and simplistic compendium of celebrity and politician name checks, at times approached an unkempt, personalized “what the hell” cadence.

Topic A on Mr. Leno’s comedy agenda was, of course, the strike itself. Observing that there were likely “more people picketing than watching” the broadcast, Mr. Leno respectfully acknowledged the worthiness of the writers’ demands and forged ahead, describing his strike-breaking creative process as one in which “I write jokes and wake my wife up” in order to try them out. Taped bits about the dubious character of the “Tonight Show” crew and a travelogue of a mythical shantytown where Guild strikers were forced to live, didn’t cover much new comic ground. But a subsequent audience question-and-answer session saw Mr. Leno extemporaneously bite the demographic hand that feeds him when he acerbically mocked the “family-friendly Vegas,” Branson, Mo., and retiree Valhalla, Daytona Beach, Fla., arguably the host’s fan-base and aesthetic capitals.

For its part, the WGA told Mr. Leno on Thursday that he violated its rules by penning and delivering punch lines in his monologue.

On CBS, meanwhile, David Letterman, whose production company, Worldwide Pants, struck its own deal with the WGA even while its parent network continued to bluster about the “unfair” digital media residual demands that are at the heart of the Guild’s grievances, fairly wallowed in his program’s status. In Mr. Letterman’s words, it is “the only show on the air now that has jokes written by union writers.” Opening with a high-kicking chorus line of Radio City Rockettes carrying WGA picket signs, whom Mr. Letterman introduced as “the Eugene V. Debs,” and featuring a top-10 list read by 10 different striking writers, Mr. Letterman’s return broadcast was so exuberantly pro-labor that he may as well have had Clifford Odets on the payroll.

Mr. Letterman’s capitulation to the Guild carried the additional strategic advantage of freeing the host’s bookers to engage SAG members as guests, something that Messrs. Leno and O’Brien cannot do without asking them to cross a picket line. Mr. Letterman’s lead guest, Robin Williams, possessed a considerably different star power than Mr. Leno’s initial couch visitor — Republican presidential candidate Mike Huckabee, who, earlier in the week, claimed he did not know that he’d be crossing picket lines. The fact that Mr. Leno’s second visitor, the personality chef Emeril Lagasse, has never made a movie and therefore apparently isn’t in the strike-supporting Screen Actors Guild, is something that both the “Tonight Show” staff and filmgoers everywhere can be thankful for.

Mr. O’Brien’s strike show was just as unabashedly pro-writer in word, if not deed, as Mr. Leno’s. But where Mr. Leno exhibited an oddly infectious cool in the face of having to take a more seat-of-the pants approach to perhaps the most regimented hour of live-audience TV in history, Mr. O’Brien was nervous, conflicted, and didn’t care that anyone knew it. In his opening monologue, he sarcastically apologized for the fact that “Americans have been forced to read books and speak to one another” in the absence of late-night TV, before wondering how he would fill his hour without his usual comedy segments.

The answer was “awkwardly.” Mr. O’Brien so completely embraced the anxiety of it all that at times he appeared short of breath. Guest comedian Bob Saget made the most of the polished misanthropic persona he displayed in “The Aristocrats.” Together, he and Mr. O’Brien doggedly maintained a facetious “what a train wreck” stance that wasn’t completely supported by the show itself. “Don’t the writers come up with all your curse words?” Mr. O’Brien asked after Mr. Saget courted the seven-second delay multiple times. Musical guests Robert Gordon, grown hulking and clay-footed since his CBGB’s heyday, and Chris Spedding, the valedictory British pub-rock guitarist, spoke to Mr. O’Brien’s eclectic musical tastes, as did a sketch in which the host performed “Sunshine of Your Love” on guitar.

Shaggy, shambling, and personable, Mr. O’Brien projected a goofy magnetism of which he seemed completely unaware. A brief segment devoted to the host’s “strike beard” was particularly amusing (as was the similarly bearded Mr. Letterman’s suggestion that he might shave off his own strike beard “on Conan.”). Similarly, Mr. Leno revealed the kernel of personality long buried by his monolithic, steamrolling, LCD shtick. As talk-show entertainment, both NBC programs were the equivalent of NASCAR races, where the crashes were many and mostly unspectacular. But until NBC and the rest of America’s media conglomerates come to their senses and grant the Writers Guild rank and file the residuals package it deserves, non-lethal comic crackups and flameouts like those on display Wednesday night are all that TV night-owls have to look forward to.