I get confused a bit by this "you can't upgrade it arguement so buy a model that you can upgrade". Seriously, how many people do you think pull old parts out of a notebook (as a percentage of total sales) and replace then with higher capacity or more memory parts? I doubt it is even 1%, yet many who write here are concerned that they'll get "stuck" with the technology they bought.
My 5 year old Core 2 Duo recently had a system board failure. It wasn't covered by the extended warranty so I had the HDD removed and ordered a new computer. I doubt it made sense to put a new system board in when the rest of the computer (HDD, RAM, Display, processor) could all be next (remember they are all 5 years old too).
They way I deal with the obsolecence issue is to buy a bit more power, storage and memory than I need today and keep the same computer for the 4 - 5 year period I'll use it. After that, Apple doesn't have parts for it anyway.
So, on my last notebook, I had 120 GB of storage (it is about 1/3 ful), 8GB of ram and a 2.3 Core 2 Duo processor. For what I do, it had plenty of performance. My new order is a 2.6/16MB/256SSD model. More than I need today and about right for what I'll need tomorrow. I could have saved $600.00 by buying the base non retina model, but to upgrade a new MBP from the base specification to what I've ordered (aftermarket stuff) would likely be more than $600.00. So what would be the point?
My advice, spec what you think you'll need over the life of your new computer and buy it. If it needs a repair, unless you are an expert or someone who doesn't mind the risk of a self repair, you'll be happier and will have less hassle.