Whilst I'm sure this is an oversight by Watford, it's pretty out of order and could land them in some hot water! Rather misleading advertising!
As you mentioned, some people might not notice this and could now be running a machine with half the RAM they expected.
Reminds me of the time I ordered a new PC from a company (not Watford), I asked for a 939 socket mobo, but on the confirmation they had listed a 754 socket CPU!!!
I'd like to have seen the techie trying to jam that in the socket!
By the time I noticed this, it 2 days away from delivery... on calling the company they thanked me for pointing this out, then tried to charge me an extra 100quid for the correct CPU!