In my experience in prior years there hasn't been a difference in availability in award inventory...which actually is quite annoying if you're trying to connect.

For example....Often times you can find a JFK-Europe flight in Business Class, but because MIA-JFK isn't available you cannot book MIA-Europe. I've always believed that if they don't want to offer MIA-JFK in Business that's okay, but there should be different availability on the MIA-JFK leg if you are booking a MIA-Europe flight