Google has been doing some research towards a better (for some definitions of better) protocol than HTTP - the problem is that there's a truly massive installed base: of servers, browsers, and applications. As Arstechnica says:

It's for reasons like this that the IETF isn't a big fan of replacing protocols wholesale. It's much more in line with the IETF way of doing things to add the new features proposed in SPDY to a new—but backward-compatible—version of HTTP. Designing a new protocol that does everything better than an existing protocol usually isn't the hard part. The real difficulty comes in providing an upgrade path that allows all the Internet users to upgrade to the new protocol in their own time such that everything keeps working at every point along that path.

There are lots of things that could be defined as "better". The abstract "better" is the easy part.