Why did he mine to different addresses? Why didn't you just use one?
I didn't get into Bitcoin early enough to be able to solo mine, but based on my experience solo mining with alts, I'd say it's by design that the client uses a new address to fund a block it has won.
Satoshi used to say the bitcoin address are not reusable, and it's a bad practice to use the same address more than once. The right quote was:
For greater privacy, it's best to use bitcoin addresses only once.
I think this is the main reason to explain why he mine all his blocks getting the reward in different address.
Some people think the never spent Bitcoins are more valuable than the used ones, and that's because if your bitcoins are fresh, then they are untraceable.