Even though the current asking price is high for older technology, I think we've reached a point where computing power has surpassed what is required by the vast majority of people. There will always be those on the bleeding edge who desire/need more power and performance, but I would say that around 2008 or so, we got processors that were able to handle the load of most casual users. If we weren't trying to drive a gazillion pixels, I doubt there would be nearly as many complaints about GPU performance, but there is still room for growth on that front. With SSDs becoming increasingly affordable, the biggest current bottleneck in computing has disappeared. It's not as though the MD101 is running like my old 12" PowerBook G4 was on Tiger where it was using something like 40%-60% of the CPU's processing power just to run the OS. Rather with todays ridiculously bloated OS, it chugs along using 1%-5% of the CPU at idle. I can run a virtual machine without issue when I need to, primarily to demo lab software for my students and such.
I have to say that this machine is still a fully capable machine, and is plenty for the vast majority of use cases, particularly after swapping the internal drive for an SSD and bumping the ram to 8GB+. It does everything I ask of it without any issues. By the time you add a larger SSD to the retina machine, and add in all of the dongles needed to have ethernet, FW800, optical, etc., the retina machine is over $1600 from Apple, and was significantly more when I purchased my machine last spring. If I'm spending that kind of money, then I'd force myself to stow away a few extra bucks to get the 15" machine.
On a tight budget, I had the choice of stepping away from a Mac, getting a throwaway retina machine, or getting a machine that I could upgrade to what I wanted/needed. I chose the latter option, and gave up amenities such as a retina display that I felt no great desire to have, a faster TB2 dongle port, as many TB accessories are generally cost prohibitive, and wireless ac. I don't see my ISP nor my employer's ISP saturating wireless n any time soon.
These machines may not be for those who chase specs, but considering they have much the same hardware as the early retina machines, I don't see them being forced into either software nor hardware obsolesce before many of the current retina models.