He's not completely, though. @marcos had it right about co-evolution -- leaving aside any issues of internationalization, the layout of letters came from typewriters, but the layout of punctuation available was different on different computers for a lot of the early history of programming. Some of the more extreme examples were the Space Cadet Keyboard used at MIT, and APL which more or less required you to use an APL-specific keyboard in order to be able to access all the special symbols that are part of APL. Here's an APL program:

⎕CR 'ProveNonPrime'
Z←ProveNonPrime R
⍝Show all factors of an integer R - except 1 and the number itself,
⍝ i.e., prove Non-Prime. String 'prime' is returned for a Prime integer.
Z←(0=(⍳R)|R)/⍳R  ⍝ Determine all factors for integer R, store into Z
Z←(~(Z∊1,R))/Z   ⍝ Delete 1 and the number as factors for the number from Z.
→(0=⍴Z)/ProveNonPrimeIsPrime               ⍝ If result has zero shape, it has no other factors and is therefore prime
Z←R,(⊂" factors(except 1) "),(⊂Z),⎕TCNL  ⍝ Show the number R, its factors(except 1,itself), and a new line char
→0  ⍝ Done with function if non-prime
ProveNonPrimeIsPrime: Z←R,(⊂" prime"),⎕TCNL  ⍝ function branches here if number was prime

Things became much more standardized when the IBM PC's keyboard became the norm, and were formalized in 1995 with ISO 9995. Then once it stabilized there was a strong incentive for both language designers and keyboard makers to stick with what everyone was used to so they could keep working with the other. But it wasn't always that way.

Edit: Here's what things looked like on an IBM 3276:

(Full size image)

Fun fact: the standard qwerty layout was made to slow typewriter typing down by putting common keys off the home row and apart from each other. This was done to prevent the little key arm thingies from colliding and jamming when typing quickly.

EDIT: Apparently this is not a fact