If you're going in that direction, I'm almost certain that it would've been gone if there was any pattern with the private keys.

Satoshi was mining using the earlier versions of Bitcoin-qt and thus you'd want to inspect the source code of the earlier clients for any possible weakness during the generation which I can say, there isn't any. I highly doubt that the private keys were not generated randomly; he would've wanted to test out the entire generation to ensure that it's working. If it was weak, then one of the many machines running the generators for weaker keys would've cracked it already.