Good point. I don't get that sense about the rest of the industry (as much), but twitter seems like a good example of a company which is "breaking the heuristics" - they got wildly popular via SXSW, which has many influential minds, but also hugely inflates the growth-to-usefulness ratio. They used that bump to raise enough money to do enough PR to get Oprah and half of Hollywood on board. This let them continue growing until this coming valuation. Throughout, they've struggled technically, leaked documents, and just haven't polished their UX enough.
Facebook and Google, on the other hand, have been growing out of being useful to their users, with no comparable technical issues (I'm hoping the FriendFeed acquisition does some good things for Facebook's architecture).