I wonder if it’s to break away from the mindset that everything is “www.blah.com”?
The theory is that you’ve got machine-name.domain.type (oversimplifying). The www bit became commonplace because everyone copied everyone else; early sites were web. and alsorts. Similarly .com, it’s what the public expect.
The BBC is a good example here. Radio 2’s website is http://www.bbc.co.uk/radio2 which is just clumsy, having an entire radio station relegated to a folder on a bigger site. What it really should be is radio2.bbc.co.uk but it can’t be because that’s not what people expect. (EDIT – case in point, the forum filter added http:// to the first two examples but not the third)
Extending that example, the BBC have applied for a .bbc TLD under the new rules. So speculatively, they might then move to http://www.radio2.bbc or something. Which in the grand scheme of things doesn’t change much, but it’s a snappier way of doing things whilst keeping in line with what the great unwashed expect a URL to look like.
Personally, I’m of mixed opinion. “.com” being synonymous with “.co.us” should have been stood on in the 90s. Either it should be a free-for-all or it should mean something, this halfway house is messy.