I'm not really in favor of citations (unless it is a direct quote) in blog comments - a clear, well-reasoned argument is better and most peoples attention and interest is limited and therefore so is the length of post they are likely to read in the first place. If a comment piques your interest, or simply your curiosity, Google Scholar can provide support (or disproof) readily and to a much greater, and especially more broad ranging, extent than is possible in a comment.
ADDED: Thinking about this comment, I realized I could be taken as arguing against citations in general which wasn't what I intended. I just don't think requests for citations by replying commenters is worthwhile.
Fair enough. However, your preferences may simply be different than mine. I highly appreciate it when a person takes the effort to provide links to some of their sources for various facts, which don't necessarily have to be from Google Scholar (although that can be a plus). Obviously there is a limited amount of evidence than can be included in a comment, and most comments are not going to be able to provide enough evidence to exhaustively prove their claim. But to me some is better than none (where applicable--some responses don't lend themselves to c...
To me the following points seem hard to argue against: