Don't read too much into this
This is a support page, not a sales page.
There are government and school contracts Dell has which they are contractually obligated to sell and support all computers under that customer -- this means that Dell resells Apples in those specific situations, and supports them as well.
Showing it on the public support pages is a gaffe though, unless they are weeding out the Dell owners who have hacked OSX x86 and put on their Dells, in order to say "Sorry, no warranty for you, sucker."