That depends entirely on what deal you signed. If the deal says "this is the price - period" then you're correct. However, the paperwork almost always indicates that incentives are based on what is in effect at the time of delivery and if you're buying based on an invoice or msrp price and that changes then of course the price will change.
Incentives come from the mfr, not the dealer. The dealer has no control over them. If the dealer wants to give you credit for incentives that you may or may not actually receive, that's up to the dealer but it would be stupid for the dealer to promise you a $1000 rebate that Ford won't give you since their profit margin on the vehicle is probably less than that.