You're not wrong in that assumption, but Apple has made it abundantly clear that jailbreaking the thing voids the warranty. Trying to cover your tracks and hand it in on warranty after you've knowingly done something that invalidates that warranty is despicable, dishonest, and is only costing Apple money (and believe me, they lose a lot of money on trying to make people happy).
I for one would like to see them be able to save the $$$ and bring out some kick ass new stuff in the upcoming years. How much of the price inflation of Apple products is built in because of the terribly finicky customers they seem to attract. People expect a free repair 6 months after warranty expires, and oftentimes Apple caves and gives it to them.
If you want to jailbreak, go ahead, knock yourself out. But at least have the decency to be honest and not expect Apple to stand by the thing anymore.
SLC