I disagree. Both Yahoo and MSN are getting better while Google is getting sh*tier on every version. They can even check wich pages are fake, full of random text, and use their ads. Do a search for "free mp3" on Google for example. The first 20 pages will be like 20lettersubdomain.domain.com/30leterheres results. The worst part is this: Create an original content page. If someone else put your article on their web site after you,you site will never - ever be on top search result for the article. Thats just one example.
I hope this does not happen as I use the Yahoo store platform which I think is great and I really don't want any kind of disruption there
And neither did Google. Imagine if they prepend each video with a short commercial for say $0.023. Multiply that with a few billion video viewings per month and they have not wasted anything. Google is not a search engine. Google is an advertising company that is branching out past Adsense ads.
I think you have nothing to worry about. You can see that MSFT is good at backwards compatibility when your Windows XP runs 1994 DOS apps nearly unchanged. They won't disturb the Y! products in any way, IMHO.