Soooo... what stops someone from taking their 26Mhs out of the network for 1hr and letting difficulty drop.
Then, throwing it back in after the drop?
He can do it indeed but it won't help much because the difficulty will rise again in a few blocks. So they just let it hash away for a few days non-stop.
More people mining ValueCoin now.
News of going on exchange is a big motivator.