I'm the same, I don't think I've ever had a cull of my friends list. The few people I've unfriended have been because I've not agreed with the way that they've posted/behaved. :-)

I also don't always have time to comment, but I do try to read everything on my friends list. :-) It's nice when you get a comment on your entry, but it's not essential, and it's nice to see what's going on for people online. :-D