You might not have to buy it from them directly, but you can't avoid the fact that they still have to be Verizon approved. This eliminates the ability to buy a generic phone, or a competing carrier's phone entirely. I can't go to Samsung and buy an unbranded phone and expect to use it on Verizon.

Incidentally, I can buy gas for a Lexus or a Chevy from practically every gas station in town, but I can't buy a phone and expect to hook it up to just any carrier.