Le sigh... With all due respect, are you trying to pick nits or did you not fully read my Post? I didn't say every size of every component would fit.
Most PSU's fit fine. Perhaps you've a slightly larger one or you're doing it wrong.
It makes perfect financial sense to make MoBo's proprietary in Dell's case. Again, I didn't say everything was interchangeable, simply most parts were. And if you were buying a pre-built system and were going to swap out the MoBo and Case, then wtf bother with a pre-built in the first place? Also, you can buy BTX Boards, in case you weren't aware.
And...you can buy HS's without fans. Granted, there's a bit of measuring involved to determine what size you'll need, but again, they are readily available.
How many different length-sizes of GPU's are there? Width-sizes? Height-sizes? Really now, if you know enough about video cards and how having multiples ones will (however laughingly little) increase performance, chances are you wouldn't be buying a pre-built in the first place.
There was a time when I did all of that on almost a daily basis. A part breaks (be it from a Dell, HP, self-built high-use system), I either ordered through the Parent Company or online (whichever was cheaper), then plugged in. Simple. No magic involved, no soldering, no bending things to make the new parts fit...just...plain...simple.
WTF is it with people jumping down my throat when I stand up for Dell (or all pre-built systems for that matter)? But anyway, seeing as how you're new to CF...welcome