The Olympics were supposed to be NBC's big profit engine for this year. The unit has been something of a disappointment to parent General Electric (NYSE: GE), but one event could have changed that.

Indeed, NBC's ratings for its Olympic programming seem to have been outstanding and its broadcast revenues for the event may set a record for TV ad income for sports programming.

But internet revenue for NBC's coverage may be remarkably small. According to The Wall Street Journal, "NBCOlympics.com will generate just $5.75 million in video-ad revenue from the Games, according to estimates from research firm eMarketer Inc." Some of the disappointing numbers could come from the decision to run only a modest amount of coverage on the website, but the problem may by much greater than that.

Web video may be a bust, at least from a revenue standpoint. There is more and more evidence that points in that direction. YouTube has certainly been a huge disappointment for Google (NASDAQ: GOOG). Viacom has struggled with making big money off the online version of MTV. Video has done very little to bring extra revenue to Facebook and MySpace.

The problem with selling video commercials on the internet could be that consumers have come to expect that everything online is free. Banner ads and search ads are easy to avoid as there is nothing active or intrusive about them. Video ads often start to play whether the person online wants to see them or not. That may lead to a rejection of the experience altogether.

Making cash on web video may never work. The media companies just don't want to admit it.

Douglas A. McIntyre is an editor at 24/7 Wall St.