Blogging interactions are similar to real life interactions, in that the better you know a person the freer you feel to do away with the social niceties and say what you think.
If, for example, you were at a party and a complete stranger came along and started boring you about, oh, let's say trains, you might make a few polite noises, maybe ask a couple of questions and generally fake an interest so as not to cause offence while surreptitiously scanning the room for an escape route. If it happened to be a close friend or family member you would be far more likely to roll your eyes and say "oh god, not trains again, can't we talk about something else for five minutes?"
As I work my way through the morass of blogs, a similar pattern can be observed. When people don't really know the person behind the blog they leave friendly, harmless comments. (Unless they are trolls, of course, in which case they leave very rude comments indeed). The sort of comment you can't possibly take offence at. "You're so funny" or "Lovely pic!"
You can spot who knows who behind the scenes from the banter in the comments box. In-jokes appear. Good natured teasing. It is even possible to spot who is shagging who behind the scenes from the laughably inept "smokescreen" comments lovers leave for each other. "Oh ho ho, I bet you're just the type of naughty girl who would stick a cucumber up her lover's arse. What a very lucky chap your man must be!" I read these types of comments and think "why not just wee all over her blog and have done with it?"
So, if I turn up on your blog and disagree with you, if you find me sitting in your comments box, sipping wine and spouting forth on all that is wrong with the world, giving my cynical and unpopular opinions, take it as a compliment. It means I think you are probably intelligent and likeable enough to handle a comment of substance and mature enough to relish something less bland and meaningless than I offer to party bores.