In two years, the architecture will be through another full cycle (Haswell in 2013, Broadwell 2014).
On top of that, both SSD's and Retina-display will be cheaper. This is compared to recent upgrades where really the only marked difference between lines from a consumer perspective was quad-core vs dual core and the video cards.
And you can theoretically upgrade the current Ivy Bridge MBP and Sandy Bridge early-2011 MBP to 32 GB of RAM using dual 16 GB sticks (not produced now for laptops, but could be in two years time). You can't get that same versatility with the Retina MBP because of the soldered RAM. So assuming that 32 GB becomes the upper-limit and 8 to 16 becomes the standard, one won't be able to customize the Retina in a way that's more beastly or on pace with the current product that will be available in two years. Whereas you could you do aftermarket upgrades to drive up the cost of your laptop, you really can't do much with the Retina version. Cost of replacing the battery is higher than older MBP's, and so is upgrading the hard drive as OWC is I think the only aftermarket manufacturer. Keeping pace spec-wise is thus more costly.
Barring huge innovations that might drive up the cost like the Retina has to this generation, I think the 2014 MBP's would likely come down in price and by doing so drive down the value of 2nd-hand 2012 MBP Retinas. A new MBPR (512 GB, 16 GB RAM, 2.6) costs around $3000. 70% would be $2100. In two years, I figure that Apple would have a new 15-inch Retina laptop with faster processor on new architecture, better video card, 512 SSD (by default), 8GB on a fresh battery around $2300. Obviously that would increase with RAM upgrades.
My point is I'm not sure I'd spend even $2000 on a computer that's already two generations behind and doesn't have much capability to upgrade to higher capacities.
In my experience (small computer store, doing such stuff on commission among other things), buying a second hand Mac and some add-ons (battery, disk, RAM) often went hand in hand...
I bought my 2010 MBP almost exactly 2 years ago for $2700 + ~$300 for an SSD + drive enclosure. Today I'd be lucky to sell it for $1500 considering you can get a 2011 MBP refurb for that price.
That said, pick up a $1,500 MacBook Pro and you shouldn't have any trouble selling it on for $1,000 after two years of ownership. Even better if you bought it with a student discount, and it has a three-year warranty (included with the student discount, at least in the UK).
It's something people often don't consider in the 'Mac vs. PC' debate. Yes, a MacBook Pro may be $200 more expensive than a similarly specced laptop from another manufacturer, but it's the total cost of ownership you should be considering, and PCs tend to depreciate an awful lot worse than Macs...
I'm sorry, but I think you are quite mistaken on this one.