There is a difference between configured and made-to-order. The Consumer Protection (Distance Selling) Regulations 2000 were made with custom made items in mind.
Take this weekend- I ordered a bookcase, specifying width, height, depth, shelf height, wood stain etc. If I were to return it after delivered the seller would be unlikely to get anyone else wanting that exact bookcase.
A MacBook with a RAM and hard-drive upgrade would not be covered by this as Apple would easily be able to sell it on. An iPod with a custom engraving would probably be covered.
http://www.legislation.gov.uk/uksi/2000/2334/made/data.pdf (Regulation 13)
http://www.oft.gov.uk/shared_oft/business_leaflets/general/oft698.pdf (Section 3.38).
So if any UK peeps see this in the future remember your statutory rights, irrespective of what Apple says!