Twitter is extremely startup-like in one critical respect: their attention to how the community is using their product. That's how they became huge. It's the fact that they became huge by focusing on this while others who happened upon the same space did not do this, and thus did not become huge, that wins them respect in the startup realm. Much of what you call their risk-averseness comes from this desire to follow rather than force their users. It's a lesson many of us would do well to learn and, I suspect, one of those things that is far deeper than appears on first sight.