It's less about the Colts not accepting trade offers for Luck and more about no NFL team being willing to torpedo their franchise for nearly a decade for the luxury of having a franchise QB.
THe Skins for instance gave up potentially a top 10 pick or better for the next two consecutive drafts for the right to select RGIII, and even now there's talk if Washington isn't a legit playoff contender soon there's a possibility RGIII could be gone after his rookie contract is up in four years.
That would DESTROY the Skins franchise in the near term, if not longer.
Everyone has a price, but no team would be willing to pay the cost to acquire Luck. Why would you??