But the dell also has a more powerful processor, graphics card, higher storage capacity, higher resolution display, and in the UK the price is still cheaper. So I want to know what you pay extra for in the MacBook pro.
I'm in the US, so I can't speak to UK prices. If you actually look at the same config machine (same ssd size, etc), it ends up being this:
http://www.amazon.com/Dell-XPS-15-T...id=1420950558&sr=8-1&keywords=dell+xps+15+ssd
That's maybe the closest PC laptop out there to equal a macbook pro 15 with nvidia graphics. Apple wins a little on having a fancier processor, but Dell wins on a little higher resolution display. Either way, the mac is still a couple hundred USD more expensive. What are you getting for that extra money?
One could argue that you get a better keyboard, trackpad, battery life, 3x3 wifi, magsafe power cord, etc. These are all good arguments, but that's not really going to convince a PC guy to go with the macbook pro.
You're paying for software. When you get a mac, you get free upgrades to OSX for as long as your computer is supported. For reference, the newest OSX still runs on my old 2007 macbook pro. Basically, you get free upgrades to OSX for the life of the computer. On the PC side, you pay for updates to Windows. OSX also comes free with a lot of good software from Apple, like iphoto, pages, numbers, keynote, imovie, etc.
So, it's not just a hardware thing. You're getting a lot of good software with the whole package.