The bitcoin you get also varies according to the number of users in a pool. More members means less bitcoin.
I use deepbit as backup while i mine in slush. In deepbit(0.04000) i get less for same hashes than slush(0.06000). Reason deepbit has more members & the mined coins divided to more members than in slush.
I also tried with mineco.in, where i get more bitcoins/block than slush ~0.2234, but when i get coin is the question.
You cannot compare you per round payment from one pool to another. While deepbit does pay you less per round for a given hash rate, they will also be solving more blocks within a defined amount of time because of their higher collective hash rate. (All other things being equal) A fair comparison would be the amount of payout you get per day for the exact same hash rate.