Important not to underestimate the 'upgradeable' aspect. The extra cost to order a T560 with a 512gb ssd instead of 500gb HDD is $380 while a 512GB ssd is available from $130 at newegg. You should just order the base HDD and RAM, put your own parts in, and save hundreds of dollars
In your source, it lists $1499 vs $849. Not so comparable to me. Also IMO the XPS has a bit of a 'premium' price tag to it. A similar hardware configuration on a Thinkpad T series would be significantly cheaper