The only thing i find odd about this is that, unless you are a SERIOUSLY detail oriented person, a high-end prebuilt is going to be better put together than if you did it. And likely uses premium parts.
Keep in mind im talking like.. Origin PC or someone similar where you are DEFINITELY not getting your moneys worth - but if it was bought for me, i'd use it. They cable manage better than i could ever hope to (and i would certainly hope so given the 500+ over the MSRP on parts you're looking at).
For the "average" prebuilt, sure, im with you.
But if anyone wants to send me a 5,000$ Origin prebuilt or similar...
Yeah, ill just be keeping that.