Why would anyone post their credentials to a site like this?
It doesn't matter what the disclaimer says, I've got my credit card connected to my account. Also, the domain name (spotifyontheweb.com) is registered trough privacyprotect.org.
That's pretty hard to do though: providing valid demo Spotify Premium details would be just the sort of breach of TOS that would cause spotify to come down on the site like a tonne of bricks; and non-real Spotify Premium details would be almost entirely pointless (the underlying library requires valid credentials to do anything).
Why would they use something that's similar to Spotify when they could use Spotify? The number of times I'm on someone else's computer and go "Oh, I'd really like to listen to some super obscure track not already on my MP3 player/smartphone/Kindle/what-have-you" are virtually nil, and competitors lack the huge selection of music that Spotify has.
That's not correct. We7 isn't just another web radio service. It absolutely is a service where you can listen to whatever you want, with a fairly decent selection of (major label) tracks. The major advantage over Spotify up until now has been the fact that it has a web interface, although I do take your point that the UI is pretty horrendous.