But why couldn’t they release it at the stupid $900 price point, but then offer a $100 - $200 Steam voucher along with it?

I didn't think about this; actually a good idea to "force" people into buying Steam and getting into the eco system. Really good point.

Edit: I just read another reply with a really good point. They could just sell the vouchers, even with a slight discount. So a really good point is beaten by another really good point. :D