I used to work for Dell's AES -- American Enterprise Support -- in support of the Precision line of laptops and desktops, along with servers etc.

For the most part, Latitude and Precision laptops were exactly the same hardware. Same motherboard. Same graphics. Same CPU. Same Memory. Different emblem on out case. Heftier price tag so you had better (American) support.

On the Precision 5510 site I'm able to tweak CPU options, RAM, disk. The XPS 15 site, I can only pick from stock builds (and a bunch of upsell addons).

The Precision 5510 site also has the option to pick Ubuntu and avoid the MS tax. Not so on the XPS 15 site.

I think you can look at it from a website usability mindset: XPS 15 site is simplified for consumers and Precision robust in options for business.