the inner workings of them are made by the same people so what difference does it make if it's a Dell or Compaq etc, your just paying for the name.
The inner workings are not all made by the same people. Yes there are some large assemblers such as compal mitac and foxconn but the inner workings are designed by in house teams to meet particular requirements. Even across ranges, the workings of a Tecra and a Satellite, or a Compaq Presario and a HP Business Notebook, and especially the cheap PC world Sony and the top of the range carbon fibre ones, are hugely different.
On top of that you pay for after sales care, and with laptops you'll often need it, especially if used on the road.
I have a range of them to hand, my main PC is a Tecra M10, my previous one (in use by no. 2 son) is a Tecra A5. I have a Sat Pro for No 1. son. I also have an inspiron 620 or two lying around. Dell have annoyed me more year on year with diminishing support, eventually forcing me to replace a 3 yr old server due to unavailability of parts, and tell a client that his 250 quid laptop needed a 120 quid keyboard to fix it, and other things. If you get a good one, you're fine.
HP support will send parts out in advance if they fail. In fact if you have fail prediction on the storage systems they'll send them out before they fail. Some toshibas have a money back if fail in warranty scheme. Dell don't give a monkeys about small business or individual customers.
Hence my opinion. Pay the money and get quality, otherwise save the money so you can replace the 300 quid one from the supermarket (there are some great hi-spec lo-cost deals there) when it fails.
Don't even get me started on Samsung UK support!