This week’s announcement of Google’s ‘advertising, technology, and research partnership‘ with NBC Universal has got everyone talking again about just how important Google might become to TV advertising. And since I’m an advertising analyst who also recently spent a couple years covering digital TV, it’s something I’ve been asked about a few times. My take: while there’s room for Google to make TV ad buying more efficient and accountable, there’s only so much you can do to target ads on TV — and so Google can’t, and won’t, cause nearly the upheaval in TV advertising that they did in online advertising.

Google’s dominance of online advertising is based primarily on their ability to target relevant advertising to consumers. But it’d be incredibly difficult for Google (or anyone else) to ever target TV ads nearly as well as online ads, for several reasons.

First, there’s no expressed intent in TV viewing. When you search for something online, you’re expressing an interest that can often be answered with an ad. But when you consume content (online, or on TV, or anywhere), there’s typically no expressed intent. We already know that Google’s content-targeted online ads don’t perform nearly as well as their search ads, because advertising targeted by context isn’t nearly as accurate (or actionable) as advertising targeted by intent. Google’s targeting of TV ads will have same problem as their contextual online ads; the lack of expressed intent will mean that the targeting is less effective.

Second, and crucially, TVs are shared devices. Think about how people watch TV: quite often, there’s more than one person in the room. When there’s more than one person watching TV, it’s unlikely that any single ad will prove truly relevant to everyone watching. (And if a single ad is relevant to everyone watching a certain program — say, football — then advertisers don’t need Google’s targeting; they can hit that target by simply buying spots during football matches.) Even if there’s only one person watching, it’s difficult to use past viewing behavior for targeting — because Google can’t be positive whether the person watching at any given moment is the dad who usually watches sports, or the kid who usually watches cartoons. (Unless, of course, sports or cartoons are what they’re watching at that moment — in which case advertisers can again simply buy spots during that type of programming.) The bottom line is, one-to-one targeting simply can’t exist on TV like it can online.

It also doesn’t help that TV delivery platforms aren’t as conducive as the Internet to ad targeting. Again, I’m an advertising guy, not a TV platform guy — but last time I checked, you needed IP delivery to do pinpoint targeting on TV. The problem is, Jupiter expects IPTV to grow pretty slowly, and most cable operators still don’t use IP delivery. And I’m not sure it’ll ever be possible to do real pinpoint targeting to anyone who primarily uses terrestrial or satellite TV (as the majority of European households do).

So the one thing Google does best online, that they made their reputation and their fortune on — pinpoint ad targeting — will be all but impossible in TV for a long, long time. One day, if all TV is IP-delivered and people log into their TV sets for individualized experiences, then Google’s online targeting tactics could work on TV. But that day is a very long way in the future, if it ever happens.

Without the ability to target ads on TV as well as they do online, Google is left trying to introduce efficiency and accountability into the TV advertising ecosystem. And that’s a role in which they may well find success. Networks both big and small would be pleased to see a more efficient way to sell their lower-value inventory, and we know that Google’s marketplace and bidding system can help networks get the best prices for that inventory. Further, advertisers would love to know how many viewers really see the ads they’re paying for, to help them make their future media buying decisions. Google, intelligently, seems to be focusing on just these features.

Basically, it looks like Google is building AdSense for TV. And while that’s useful, and offers a positive step forward for advertisers and networks, it’s nowhere near the type of revolution Google’s paid search model brought to the online advertising space.