Ok, so I got it now after thinking a long time.
After third try I finally took it and immediately started a premium account. It's a way expensive but I've been glad about Spotify.
Seems like most of the bands or record companies that have prohibited uploading their material on YT have in turn allowed it on Spotify. Or looks quite like that. Well, as we know anyone could go and upload the stuff there, create playlists of their favourite bands, but at least they're not removed from there.
I don't believe using Spotify would prevent me of buying CD's, no. (I've become more and more an album freak and I'm satisfied only when I finally get a real cd or a collector's choice album in my own hands!) At least, there's even some profits the artists can get when you compare it to YouTube that is a total zero that artists get. However, I hope in future the artists get more profits of usage of Spotify and such.