Is it just because they have way too many left over from last year and they're trying to get rid of excess stock? Or are they paving the way for something new? Actually, it's almost definitely the former, but this is an Apple post, so I just thought I'd throw in some random speculation so I'd fit in with all the other online news sites.
If you're interested, the clearance sale will run "while stocks last".
[Optus – Thanks Sonny!]