Which is great. But it's comparing apples to oranges (if you'll excuse the pun). I chose equivilent hardware.
No problem
Fair enough, but that is what my point is, you have choice, you can get better hardware for the same, cheaper or only a bit more expensive.
Yes, I did. I chose a high end all allu case that would fit an e-ATX motherboard. A cheap plastic case is not equivilent to the Mac Pro case.
Well personally the case wouldn't be my first choice, don't like the looks of it one bit, I am sure that there would be a nicer aluminium case (than that li lian one) somewhere for a lot cheaper that would fit the motherboard. Also IMO, most of the plastic cases are the far nicer looking ones than the aluminium cases and also feel like higher quality to me.
Maybe, but you may stuggle to fit two large coolers on a single motherboard, hence the water coolers.
True, but as said, there must be cheaper coolers that would fit or you could use the corsair H50, you can get it somewhere else for a good bit cheaper.
Comparable hardware. This is a workstation not a gaming machine.
Then is really much point in spending this much on a PC/mac etc. if your just going to use it for a few word documents, web browsing etc.?

Unless you want it for encoding etc.
Plus having a good GPU also helps improve the speed through out the system I have noticed especially for GPU acceleration in web browsers etc.
The Mac Pro came with 6gb as standard, the Dell 4. Were I being picky I would use much more expensive registered RAM as they do.
Yes I know that, however you have the choice of having an extra 6GB of RAM for very little extra (due to this time for excellent pricing on all memory) and crucial is a very good memory brand, maybe not as well regarded as corsair and kingston but I would much rather have the extra 6GB, granted it would be useless for gaming etc. however very handy if you multi task with a lot of programs open, photoshop, encoding etc.
Because you get wireless peripherals with the Mac Pro.
Again, you have choice

, but if you want, you could probably get a logitech wireless set for the same price or a bit dearer which would be better.