Caveat Emptor.

If you buy a Dell, HP, Gateway, etc., expect to only be able to upgrade cards that go in the expansion slots and then only to the specific models supported by (and usually available from) the OEMs for that model. The only way you guarantee upgrade compatibility is building your own.

Regarding the "de-populated" motherboards, this is NOT unique to Dell. All of the major OEMs build systems that cheap because they ALL de-feature the boards to support only what the system specs say they support. Lite-on, Foxconn, Qanta, etc. ALL of the major ODMs remove parts if it reduces costs. This should not be a surprise. It is MUCH more prevalent on the ultra-cheapie boxes but even the high-end systems from them are limited in what upgrades they support.