I'm personally too far from those negotiations to offer any likely-pivotal insight (such as a concrete quantity), but my very rough understanding is that there's some critical volume beyond which a customer basically becomes "made" with the Xilinx/Altera sales channels via a financially significant design win, at which point sales engineers etc. all but have a blank check to do things like comp development boards, advance a tray of whatever device is relevant to the design, etc..

Basically, as George Carlin put it, "it's a big club, and you ain't in it".