Let's face it; you can end up with a borked (enter part name here__________________) whether you buy a pre-built or home built computer. To each, his own.
This is pretty true. For some that emails, general office stuff, and browses, a Dell will do wonders for them. Gaming is a different story. Only their higher end stuff is worth investing in if you want to game, but thats if #1 you don't know how to build #2 some other excuse. A home built 'gaming' rig is going to be quite a bit cheaper than a 'gaming' rig from another company. Now for a home built 'office' computer, if you can't reuse software, a Dell/whatever is going to be cheaper on the front end.
I like to know what parts are in my system (plus I enjoy doing it). If I order a Dell/whatever, I don't know what model/mfger of the mobo/PSU/etc are for the most part.