Here's what I noticed

http://blockchain.info/block-index/400004/00000000000000919cffff6ed0b97f2323b262f9e2912a62ccd24cc3047191b3

Timestamp
2013-07-17 03:24:07
Received Time
2013-07-17 03:26:05

EVERY block solved by AM takes TWO MINUTES to get received into the network. That is about 4 times longer than most other nodes:

http://blockchain.info/block-index/400003/000000000000006319cd633a4f0ab60febbca002d4520fcfa57680ee2959fb5e

this one took just 30 seconds.

The longer it takes for a block to get distributed by the network, the more chance that it will end up orphaned. This is probably also the problem with the small number of transactions in AM blocks, it just takes too long for them to get to the AM farm!