That is the case yes, for spotify to work natively on iPad you have to have the premium version. For what i wanted though, which was mainly for playing spotify around my house away from my computer, I've found another way to get spotify on your iPad.
Airfoil traditionally streams non-iTunes sound from a PC over wifi to speakers. They've recently (or I've only discovered it recently anyway), developed an app for iOS that lets you stream from your PC to your iPod/iPhone/iPad. That means I can play spotify on my laptop, and listen anywhere in the house on my iPad, and plug iPad into speakers or Bluetooth from iPad to speakers etc depending on room and speaker setup.
Obviously this won't help when out of range of home wifi, but it's great for around the house. Depends what your after. Just though I'd share my findings.