Spotify has always been fairly popular, at least in the press. But it found a new wave of popularity when it hooked up with Facebook as part of the first wave of OpenGraph apps. With the help of Facebook's inherent virality, it quickly gobbled up millions of new users, many in the US where it had just launched.
But there was a price to be paid, Spotify started demanding that users sign up with their Facebook accounts. It was an obvious setback for users who would prefer to keep things separate or simply don't have an account.
It seems though as Spotify is backing down, at least in some cases, as it is now allowing users to create new accounts, without the need for a Facebook one, in Germany.
It's possible that the relatively low Facebook penetration in the country may be the big reason behind this, so it may not mean anything for other countries.