Yes, Randyh replied to this question as I also asked it earlier.  And the answer is that they are trying to use transaction times over a period of time to determine the hash rates and payments based on the changing price...

In other words when the market is volatile the What To Mine numbers get way off... The steadier the price and transaction rates over time the closer WTM is with its estimates... So WTM is really a best guess at this point and you really can't tell what your going to get until you point at some pools and see what the calculation comes back with for reward.

So right now trying to use WTM to figure out what is the most profitable doesn't work very well. I am sure it will get better as we see things settle down over time with ETC.

Right at this moment my pool is reporting I am earning more than WTM states, but over the past week it has been just the opposite... So you just have to check for yourself on the pool to validate.