Why would that make any difference in the short term?
It's not 'short term', but a long term trend. Right now Antpool reports 57.77 PH/s. Your chart at
https://bitcointalk.org/index.php?topic=104664.0 shows that DiscusFish and Antpool found about 27% of blocks between Feb 8 and Feb 14. Isn't this simply a case of smaller pools like Slush having a smaller fraction of the overall hash rate?
Cheers