As far as I can see, they're the same chassis. It seems configuration options are all that's different. Though they refer to XPS 15 as 9550, not 5510.
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.
The reason why doesn't have much to do with the specs. I've rocked Thinkpads for years, but I just can't get behind Lenovo anymore.
Anecdote time: Couple years ago (in the T410 era) I was on an IT team looking for new laptops for a small company. We got a guarantee from a Lenovo sales person and someone from their support side that we could pay for NBD repairs and they'd fix machines with Linux. When our first repair need came up, they refused to do anything until we re-installed Windows. For a bad display (it was all pink), nothing to do with Windows! We ended up keeping a spare, vanilla Windows 7 HDD around for when we needed it, but it left a bad taste.
Couple that with their more recent headlines about spyware in Windows machines, and back doors on some their mobile devices, and well... Fuck Lenovo.
My vote for Thinkpad would be fueled by nostalgia at this point. I'd give Dell the money for just trying and doing a damn fine job making Linux laptops people want to use. I've come across threads where they're supporting alt distros like Arch.
http://thehill.com/policy/technology/310812-dhs-responds-to-...