I really doubt Apple uses ECC RAM.
ECC guarantees that the RAM is exactly one gig, or 512 megs, etc. It also costs twice as much, and if not that, a great deal more.
Normally you only get it if you're obsessive, and i doubt apple would bother with the extra expense.
Every once in a while you get a goofy stick thats missing a couple megs. I had a 64 meg stick about 7 years back that was only 63.
Shouldn't be a problem unless it gets worse, or its a huge amount (someone i know has a 256 thats only like...190)