Is a blog really a blog if there are no reader comments?
It’s an interesting question, but the answer is pretty obvious. Yes, of course it’s still a blog.
As Arrington notes, most definitions of a blog is a regularly updated website with content in reverse-chronological order. I reckon that’s about right.
Comments are nice, but not a requirement. John Naughton’s blog, for example, doesn’t have comments open, but that doesn’t make his site into something other than a blog. It’s not something I would personally do, but on a popular blog, the moderating of comments could turn into a serious business. If Google allowed comments on their blog, they’d probably have to employ someone full time just to deal with them.