Maybe the question should be "What happens if javascript is disabled?".

I do think that it's important today because there are still web browsers, especially in the mobile space, where people will not have javascript or more specifically AJAX available.

I think it's especially pertinent when talking about social anything kind of sites, where people are going to be likely to try to access it from a mobile device.

I don't see it as an issue of responsibility as much as I see it as a customer service issue.