Why get a regular MacBook Pro versus the Retina display model?
I can buy a regular MBP, with a cheap HDD, open it, upgrade the RAM and replace the HDD with a SDD, all for a fraction of the price Apple would charge me. In addition, I still have Ethernet and a CD/DVD drive, in case I need one. 

As I said, you might need the retina, or you might just like it, both of which are perfectly reasonable points. I don't, and I prefer to keep my money with me, upgrading my hardware when I need it, and at the price I choose to pay (out of a range of options).  Uh, and I also hate the lack of Ethernet port.

To each their own.