One losing 3 blocks on various occasions.

The other losing 250-500 BTC by allowing a miner to test their system on the pool - a system that withheld blocks due to bugs.
That pool (slush) then hid the details about it and allowed the miner to get away with the large amount of BTC they were rewarded for testing mining with code that didn't work - the miners on the pool paid for it ... though today's hash rate on that pool proves that many of those miners didn't care about that loss that the pool hid the details from them, and the fact that the operator allowed that ... most likely for payment