I do believe it is also because of the potential for messy wiring. A PSU fan is a lot less likely to get jammed by a misplaced wire if it has a grill over it than if it doesn't. Computer components for retail sale are generally built on the principal that the person installing them is a thumb fingered moron.
Yeah, I thought of that, but it sounds very unlikely. My old computer (had it for ~5 years) had some super messy wiring and no fan grill on the HSF, yet none of the cables committed a suicide. The reason I started this thread was to know if there are any plausible reasons for not removing the grills (and use them somewhere where they're actually needed), since my wiring is pretty tidy.
It's to stop EMI from exiting the apparatus.
Oh! I guess that makes sense, but I don't think a wire grill helps much, I suppose it's the PSU's metal casing that blocks most of it? And HSF probably doesn't generate EMI?
or a chainsaw warns you not to stop the chain with your genitals.
I wish I had known about this the last time I used a chainsaw.