Not only that, but Yahoo didn't think search was important, so it's not even a real try of enhancing search with curation.
The truth is, if some company comes up with a better search engine, whatever ideas behind it are not going to sound like an obvious win up front—if they did then Google would already be doing that. Instead they'll have to create a search engine that is better, but somehow antithetical to Google's business model so that they can't just copy it, because there's no way for a startup to come up with enough resources to stay materially ahead of Google in pure search. And of course that's only half the battle; then you have to be better enough that users can be bothered to switch (or a browser deal coup).
Personally I haven't found the spam problem to be nearly as bad as the echo chamber makes out. I think silicon valley types just have a good imagination about how good it could be.
[1] http://en.wikipedia.org/wiki/Wikia_Search