But they won't. Point is if you need a powerful laptop it's likely for work and spending this kind of money on a work tool is firstly not a lot of money and tax deductible over 3 years in most countries.
The other thing of course is resale. Macs all have great, fantastically great resale value. I've just sold a 2 year old macbook for 70% of what I paid for it. This is partly down to the fact you can actually get part fro a Mac 6 years down the line... most PCs are obsolesced after 3 years and you have to rely on eBay which is hard as they make so many models.
And of course why on earth would someone who has used a macbook ever go back to a Windsows Dell.
It is not a powerful laptop. A fully spec'd dell 7710 or Lenovo p70 is a powerful laptop.
The parts part is totally false. Very easy to find parts unless the model is obscure.
Have you tried Dell precision ? A 5510 or 7710 is way better value. And can be bought much lower than msrp.
Value wise, performance wise - no comparison. And build quality is better on Dell. There is no obsession for thinness. Thus better cooling less throttling.