I'm unconvinced. A singular resource name implies a singleton resource, e.g. /account, which is a singleton as far as the user is concerned. It's a simple pattern: singular > singleton, plural > collection.

Github does all kinds of non-standard stuff like putting the requested response format in the URI path instead of as an extension, e.g. "http://github.com/api/v2/json/repos/search/ruby+testing. So just because Github has done it, doesn't mean everyone else should too.