Here's the thing. Apple is making this increasingly difficult in newer Macbook Pros.
The average Joe with a Mac (or a Lenovo or a Dell for that matter) doesn't know about RAM upgrades or SSD random seek times. He doesn't want to know. Apple still manages to deliver a laptop that will work decently out of the box for the years to come, with a reasonably fast SSD and an acceptable amount of memory for most tasks.
Now, why the rest of their product line (Mini, iMac) still ships with sub-par hardware (4 GB base memory and/or 5400 rpm drives), that I don't know. I guess they're becoming products for a more and more niche market.
That's true, but I think the point is, the people in the tech bubble are also the people making the apps.
I don't know how you'd go about testing this, but I feel very strongly that part of Apple's recent success has been due to making very developer-friendly computers in the early 2000s. The original iPhone was a joy to program for (once they finally opened it up) because it was based on OS X, which was already pretty great compared to the competition.
If programmers stop buying Macs, because they're just too expensive, too limited and unexpandable, the apps will start drying up and users will start drifting away. Maybe.
It's just hard to see who these new machines are aimed at. I see tons of students using Macs in coffee shops -- but what's happening to the low-end, semi-affordable Airs? Graphics and video professionals love Macs -- but where's an up-to-date Mac Pro, or at least a really beefy MacBook Pro? I'm a mobile app developer, I love my MBP, but if I get a new one I'd also need a ton of adaptors for all the mobile devices I work with.
Well now you see why XCode can only run on Macs. Want to write apps for the biggest and most profitable mobile ecosystem? Gotta buy a Mac, we don't care if you don't like the lack of upgradability.