The same question/comment was posted to r/bitcoin a few days ago: http://www.reddit.com/r/Bitcoin/comments/1c48u0/how_did_bitc...
This comment on that post seems to calculate the number of people mining bitcoins for the first year: http://www.reddit.com/r/Bitcoin/comments/1c48u0/how_did_bitc...
If satoshi was indeed just testing the network... why not use "testnet" or simply re-set the blockchain once you were satisfied with the results of your work and release it to individuals?
Oh, wait... because you wouldn't hold 7.8% of all the Bitcoins that will ever exist then if you did that.
Just because almost half of those first 1.8M bitcoins mined were "transferred", doesn't mean that they ever transferred ownership.