Yes and no. If you have a templating solution that works well on the client and server then this shouldn't add much complexity. Rendering the initial view on the server has the added advantage of supporting javascript-disabled clients too.
I muddled my point by mentioning Twitter - it was very nearly a non sequitur. They're supporting two paradigms but not because they want to. My understanding is that they don't have a single solution that works equally well on the client and server so they are using two different solutions.
