Hi Matt, Cryptonight can be GPU mined - do a google search for "Claymore GPU miner" - I have been mining XMR for a few months with this miner and it works wonderfully (it is about 10-20x faster to GPU mine xmr vs cpu mining it (Per GPU) - this is probably why you see some miners with a really high hashrate.
Claymore isn't 10x-20x faster than CPU per watt. In fact per watt it works out about the same efficiency as CPU mining. An Atom C2750 can get 63H/s on four out of eight threads of a 20W TDP CPU. While they're even more efficient CPU's than that. Also there's no Linux or opensource ATI cryptonight miners still as of yet. While traditionally most cryptocoin GPU miners would have used Linux and ATI cards.