I think you have seen things from and SEM view point, that is exactly how I see and hope things are
But you and I are not average internet users, we have lots of deep knowledge of how SEM and SEO works so we look for text based links rather than Javascript based link but majority of Google and Yahoo AdWord customer cannot tell the difference between text link and Javascript base.
I have a client who spend about the equvalent of 10,000 Euro with Google every month on AdWords, all he cares about is just traffic and he told me that when he spend that money he actually gets value for his money in terms of traffice, so such people do not care the basis of the traffic they just want traffic and they are satisfy as long as they make their money back.
Another reason I also thing Google/Yahoo will not go to text link ad is because it will affect organic search engine results. I have a felling they will keep the ad delivery technology as it is, the only thing I see them changine is moving from PPC to PPA as most PPC customer are not happy because of the amount of money they lose to click fraud.