Coming from me, someone who hasn't owned a Nokia phone since 2003. Nokia / Windows Phone is extremely niche in comparison to the other two. I'm transitioning because all I really care about on a phone is the camera. I originally got the 4s a while back because it was one of the better camera phones but it's been completely surpassed at this point and I don't think anything will beat the Lumia 1020 for a while.
The high price tag, the fact it's niche (windows phone) and only available on one carrier (at&t).. I think the numbers will be below expectations, but hopefully I am wrong.