I have registered several accounts on WP, but none of them are available now, they are all get banned. I think WP is very strict with users, it has a lot of limitations for posting.
You might be using these blogs to promote some unsolicited content/services. You can check the TOS of wordpress for the same at http://en.wordpress.com/tos/
Yep, Wordpress is a great platform, but if you want to monetize or do what ever you want, you need your own blog. Self hosted Wordpress is the way to go.
I would agree 100%. Never rely on content on a platform owned and controlled by someone else. This goes for blogger, youtube etc etc as well. Love many, trust few and always paddle your own canoe!
WP is actually very lenient, you must have done something very wrong. I agree with hmansfield though, it's now very easy to set up your own self-hosted wordpress blog and it's also extremely affordable.