During these four years, I have been able to: replace the keyboard (after I had improperly cleaned it), replace the battery, upgrade the RAM, and upgrade the HDD. I can give it to a family member as a hand-me-down as it not only wasn't that expensive but has a lot of newer the components that make age well.
Four years ago, I was fine with having even just having 2 GB for a bit of Photoshop and browsing on my current white MacBook. Now, even after expanding to 6 GB (the undocumented max for this model) I still get memory swapping due to the newer Photoshop and tons of tabs in Chrome. That's of course, a limitation of this model. If I had even one of the newer MBPs, I could go up to 32GB in memory when 16GB sticks come out, as I believe that this Ivy Bridge model and the early 2011 (not the late 2011) Sandy Bridge MBP's can be upgraded to 32GB of RAM despite Apple's documentation that it only goes to 16GB.
Unfortunately, because the RAM is soldered, it means I don't really have that option. Which kind of blows because in three years, 8 GBs could be closer to the normal use case, and 16GB will probably be what some professionals need, while 32 GB could become the cushy future proofed number that 16 GB is right now.
And then with the SSD, I think the idea is that some people (including myself) would rather pay for the minimum right now, and pay for the upgrade when parts come down in price. Effectively paying $600 largely for an extra 256GB (as the processor upgrade of .3GHz is quite unnoticeable for most) isn't outrageous, but I think the onus is then to front-load the costs instead of appropriately upgrade when some costs come down. Thankfully, it is possible to upgrade the hard drive (like Air), only it's just a bit more tricky than a standard SSD because there are less options outside of OWC.
The Macbook Pro Retina is a great and beautiful computer, but it's the toughest laptop choice I've had to make in my lifetime. I've always felt burned by front-loading computers ($4k PowerMac G4 which was a beautiful machine but easily underpowered after a few years, my hand-bult built $2k desktop that was outdated six months later when PCI-Express became ubiquitous) as I rarely feel justified spending $3k on something that is left behind in a short amount of time, even though I do 100% of my work on it. So I've preferred going with a bare-bones approach with upgrading components as they get more economical.