My understanding was that having a blocksize limit was Hal Finney's idea and he talked Satoshi into it after quite a bit of discussion between Satoshi, Hal Finney, Ray Dillinger and possibly others as well.  Although I'm not entirely sure if setting that limit at 1MB was Hal's decision too, or if that was someone else's input.  But suffice to say it wasn't just Satoshi acting alone.  In the early days, it's likely quite a few conversations were had via email, so we don't have reliable records of exactly what happened.