I honestly can't help it sometimes. ^^; It's partly because I'm someone who likes keeping their word, so when I say my comic will update evey x-days at y-time, I try to keep to that schedule.
It's also just because, in a weird way, I kinda like my readers. There's plenty of cool and more interesting comics out there and they decided to follow mine, so my of saying thanks is to just work hard and keep a consistent schedule.
I don't really feel too bad about lates, though. When they happen it's more of a "Whoops! My bad, fellas!", but I get what you mean about apologizing too much.