How is the weekly dividend paid out?

I've been seeing dividends of .03 BTC / week, and am confused to how they are that high.

Assuming that asicminer has 20% of the total network hashing power, they would be mining approximately 20% of all blocks.

(0.2)*(6 blocks per hour)*(24 hours per day)*(7 days per week)*(25 BTC per block) = 5040 Bitcoins per week

5040 Bitcoins / 400000 Total Shares ==> Dividend = .0126
5040 Bitcoins / 163962 Public Shares ==> Dividend = .0307

Does this mean that the shares owned by friedcat aren't earning at BTC?