but google isn't just google search anymore, so even if some competitor comes up with a "better advertising model" will they be implementing it in many domains (search, free email client, youtube) at once?
Google has a leg up by virtue of the fact it could deploy any new product massively and immediately, but that barrier to entry is hardly insurmountable. It just means the new paradigm would have to be significantly better than the current one, for the following three groups:
1) Advertisers. Companies would need to see a significant benefit to moving to the new platform.
2) Site owners. Either by virtue of UI or increased revenue, a new platform would have to offer a significant advantage to site owners to spur adoption.
3) Users. This one's basically optional, and included in 2). A new advertising platform would have to be unobtrusive enough to not piss off users drastically more than current ads, but a strong enough showing in 1 & 2 would make that less important. Ideally, a new platform would offer ads that users want to see, by virtue of being either entertaining, relevant, or both. See movie previews in theatres for a good example of this.
Google is still "just ads" even if they do have other services and popular properties to put those ads on, which is why someone else's better solution would be a threat.
Does the next AdWords/AdSense need YouTube to succeed? No.
But this "just ads" is really widespread, when someone will come with a better solution, until they reach even 1% of what Google has, Google will come up with a better solution :) And no one would like to switch from expert like Google to some new guy
Lots of companies used to be really widespread, now they're dead or dying - AOL, Yahoo, Digg, MySpace, Altavista, etc.
Google will have plenty of opportunity to fight for their position in the next round. Some companies can win that fight again and some can't, no way to know which category Google or anyone else falls in until after the fact.
Yes, there is always probability left for someone new to takeover. But it is really small, especially in this case. At least for now. While Google is making really smart strategic moves like android and chrome. And yes, Google will have LOTS of advantages in the next round for the position.
