Uhm... I'm pretty sure that's not true. While they may reject it had you overclocked it and then burnt it out by overriding thermal shutdown protections, I don't think just overclocking totally invalidates the entire warranty. This is not overclocking related (unless the reason you dropped it was because it was blazing hot because you overclocked it....)

Besides, good odds it's busted enough that even if they wanted to, showing that it was ever overclocked would be tough. And I'm quite sure the warranty doesn't even mention overclocking, so legally...

If it's still under warranty terms (time wise), send it in. Worst case they say it's not covered and send it back, not much to lose.