What!! Mac people open a case - I think I'm going to faint
As you say Richard it isn't a biggie. It's the same for a Dell and if you look at the Zens it's a case of some do offer a removable battery cover and some don't i.e they're sealed and this varies for different national markets according to the Creative website.
If I owned any of them I wouldn't mind at all going on my experience of the iPod (original 1st batch, 5 gig model). It keeps it a minimal, clean, relatively dust, grit, and damp-proof form factor. Still on it's original battery despite heavy use.
Final recommendation is to
listen for the player that suits your tastes and do it with a single pair of high quality buds or phones for consistency.
Regards
rob