Perhaps you aren't persistent enough, but Apple's 14 day return policy is simply a piece of paper that means nothing.
I upgraded my 3gs after four months, I went from a 21" iMac to a 27" after three months and went from a black 16gb iPhone 4 to a white 32gb iPhone 4 after nine months!
If you are nice, handle yourself with class and communicate effectively with the right person in the store then I would say there is a 75% chance that Apple will take your product back and let you upgrade anywhere inside of 12 months.
That's been my experience.
What Apple store are you going to??? My Apple store won't budge on anything whatsoever..