The stats are correct but the return is almost always lower on zpool than on the other pools that doesn't autoexchange.

ex:

skein

zpool.ca 24hour    payout per ghash: 0.00449BTC
yiimp.ccminer.org payout per ghash:  0.0062BTC

+38% if you mine on yiimp and exchange your coins yourself.

But zpool is more profitable than the nicehashminer..