Hikari.S
When the typewriter was first invented, the keys were in fact in alphabetical order, however they found that people had a very difficult time typing. Their fingers kept getting in the way of each other and they couldn't fast at all.
I'm not sure exactly how they measured this or any algorithm they used, but the layout of the keys, at least on English keyboards, is designed specifically to make typing easy, with fluid movements.
Your on the right track but a little off. I've heard that devorshac (totally miss spelled I know) or what ever its called was the original findings of the easiest setup of letters, however at the time typewritters could only handle so many letters per second w/o jamming up. So they re-did the layout to slow people down so they wouldnt jamm their typewritters. and b/c it was easier to keep the same layout that everyone was used to when the computer came along that is what we use today. lame but its the way it is.