Well Yahoo really hasn't changed much in the past 10 years.
And most of the others were pretty much the same.
With live feeds and google's search engine, the need for web portals like Yahoo have become irrelevant. The main reason some of those companies are even still there is probably cause they were able to aquire a bunch of other little web companies.
Google seems to be the company that waits to see where internet trends are heading and then tries to cut in front of everyone a year or two later.
They don't need to worry about legacy stuff, they're a web based company, so as long as there's internet anyone can use google's stuff.
And in the end, even if the new stuff they come out with doesn't work as they plan, they'll always have the search engine. I doubt some new search engine will just pop up that's "better" than google to take its place. If anything were to become a threat, they could just aquire it like they did when Youtube did better than google video.