Sometimes comments are very useless. For example on this question syneticon-dj comment on the original question is so incredibly useless I'm not sure if I should comment back or mark it for deletion by a moderator. The reason I am strongly opposed is because it encourages discussion that others won't find useful, I mean others won't find it useful why it is the RAM specs need to be determined. And it's not very constructive if I reply back I'd rather use a GUI than open the case, the conversation is very moot.
When comments are too chatty or otherwise not constructive, you can flag them.
With regard to that particular comment, I don't feel it's absolutely off topic. It is somewhat related to the question. Given that the post has become quite popular since yesterday, we might clean up all the comments anyway. Comments aren't meant to stay forever. They should be used for clarification, and may be removed at any time.
But if you don't want to get into a meaningless discussion, then don't—it always takes two for that.