Contradictory profitability tests

In previous posts, I asked customers to perform some tests to determine whether Prohashing was more profitable than several other pools. I also performed a test with scrypt mining in litecoinpool.org. In all of the tests about which I was informed, the conclusion was that Prohashing was more profitable than the tested pools.

If that is the case, then why have I also heard some customers say that they think they can make more money at other pools? What is different about our tests than their circumstances? Is there a miner type that I'm not aware of which creates different results?