Wow, they don't want people to spot that, do they :) I went to the signup page to verify before I posted my comment and completely missed the link, even though I was looking for it. I really appreciate them doing that - will check out their library today.
Edit: Or not. They seem to know my city better than me since my postcode is both required and invalid...
I think you meant that sarcastically, but it actually is good design from Spotify's point of view. They really want people to link their accounts to Facebook, but don't want to lose the potential users who steadfastly refuse to do so. Tailoring the language and design to encourage the desired choice is smart, even if it might not be quite right grammatically.
Edit: Or not. They seem to know my city better than me since my postcode is both required and invalid...