Well, for my needs as both an engineering student and doing engineer related work, the cMBP had several advantages over the rMBP:
Ports. I don't use thunderbolt. However, for work I need an optical drive and ethernet. For getting actual sh-t done, being directly connected to the network is actually much more productive.
User-replaceable RAM and HD - Already stated numerous times before. When looking at the retina I couldn't bring myself to pay apple's ridiculous prices for RAM and SSD space. 256GB for $2200 laptop is not worth it for me. The only I reason I got the SSD I have now is because I got it as a gift. This 250GB SSD I have now is way too small. I paid $100 for my high-quality 16 RAM.
Retina Display is useless. It's a great gimmick, but as an Engineer I don't need things to look pretty, I need things to work. It puts more unnecessary strain the GPU which is counter-productive to CAD rending and when gaming. People argue the GPU in the rMBP is more powerful than the cMBP(Gee, I wonder why🙄) but I will only see that extra power if I use an external display, which defeats the purpose of having a retina display in the first place.
The rMBP is definitely a better machine in many ways, but for my needs it just doesn't fit well. Will I eventually get a rMBP? Of course, but there is no need to force yourself onto something if you are given an option that fits your needs better.
People will jump in this thread and argue that these advantages aren't really advantages and that I could buy a bunch of $30 adapters to do the things I need the rMBP to do, but at the end of the day my needs are my needs no one else's opinions really mean anything.