You are gravely mistaken. Satoshi mined just one block for no more than six days. Furthermore that block cannot be spent, so in effect he premined 0 coins.
But (s)he did mine lots of blocks during the first month, while it was still under development and only known by those (s)he was emailing that time. Didn't (s)he?
I remember reading the whitepaper beginning of December 2008. Nobody emailed me anything, it was all public info. The news got out to the ones looking for new stuff. Then the software appeared in January, v0.1.0 alpha. I mined (and threw away) some block in February. It was a windows executable, sounded very fishy to me. It was worthless thing, making the laptop fan buzz all time.
Satoshi didn't mine lots of blocks, just made sure that blocks are still mined. Almost nobody was interested. For a whole year the difficulty was the lowest possible - 1, and the hash power couldn't produce blocks fast enough to even reach it. There was once more than 24 hours between two blocks.
In retrospect this was the correct way to do it. Too much marketing, and it would be crushed at the beginning. It was just at the edge, and managed to survive so far.
