Are you sure the price in the magazine is plus vat? Is it exactly the same? Have they maybe added some parts to make it pull up with the magazine suggestions to up the price?
Not got my mag with me at the moment but Im sure if you call them they can explain the difference. I would be sure it is likely to be less VAT.
On another point however PCA and many magazines just get given PCs to test. There are computers out there that would be faster that those in the top 10s. So go check other places. Just compare specifications. Ideally make a spreadsheet with the specs and then write down each pc with all the most vital details of them.