I was interested in what you said so i had a look back through my copies and the November C720DC you mention has a ATI Radeon X1600 card and the latest/December ad is a 512MB Nvidia 7900GTX. So while the name and chassis's are probably the same the insides are completely different. They might have sold out of the X1600 version. Especially since the November issure will have been out for about 6 weeks.
So be fair to Evesham and be realistic, specs change and how can they be reported to the ASA for an advert that is out of date.