Mike, you're right. I just looked up my parts list and there are two alternators listed, 50Amp and 40Amp or 700W and 560W.
The apparent difference is as you say, with or without ABS and heated grips, etc, etc,.
In Australia all BMW bikes come fitted with heated grips as standard, if they are available for that particular model that is. Therefore I'm used to only seeing the larger 700W alternator on machines.
Whatever, 560W is still a healthy output,and,if the machine doesn't have ABS and/or heated grips,then perhaps it doesn't matter about extra lights being a burden. It appearsthat the residual leftover output should be about the same no matter which alternator that one has!
Mick.