The first Mac I ever bought for myself was a Power Mac 8500, circa 1995 -- ancient history now, but despite its uber-boring beige box, it was a truly great machine, able to do things that most PCs of the time could only dream of. In modern terms, it was the great-grandfather of a fully-loaded Mac Pro.
More to the point, almost every feature about it was upgradable, including the CPU, which was on a swappable daughtercard. That workhorse Mac saw heavy-duty daily use, including code compiling, video digitizing and 3D rendering and animation, for more than 10 years, while computer hardware and architecture advanced rapidly. I fired it up for this article, and it's still humming along. This longevity is noteworthy enough, but even better is that with its upgrades it could have been considered nearly state-of-the-art for most of its life. With memory finally maxed out at 1GB (for a machine that first shipped with 16MB), high-speed SCSI-3 drives, FireWire and a G4 CPU upgrade, it could even be induced to run Mac OS X 10.5. (No, I didn't do that myself, but it can be done.)
The non-upgradeable MacBook Pro
Enough nostalgia. Let's jump forward to June 2012, when Apple unveiled the new top-of-the-line 15-in. MacBook Pro, with its ground-breaking Retina display, a truly drool-worthy laptop if ever there was one. It's fast, powerful and stylish, setting the standard for what a full-featured yet highly portable laptop can be. But that gorgeous package comes with a cost. iFixit, in its teardown analysis, gave the Retina MacBook Pro the lowest possible score, 1 out of 10, for its almost complete lack of upgradeability. There are no user-replaceable parts whatsoever, including the battery or even RAM, which, in a trend begun with the MacBook Air in 2008, is directly soldered to the logic board. What's wrong with this picture?
Apple has long divided its offerings into "pro" and "consumer" lines, and this divide has only diverged lately, as an ever-growing proportion of Apple's revenues and profits have come from consumer-focused products such as iOS devices - the iPad and iPhone (and to a much lesser extent, Apple TV). While power users may need and want upgrades for Macs, consumers, usually replace their iPhones, iPods and iPads, with new devices rather than upgrading their current hardware. Updates happen at the operating system and application level. In short, these are all "sealed-unit" devices by design, with no hardware-level upgradeability.