The pro-level computers -- the Mac Pro, the MacBook Pro, and the now-defunct enterprise-focused Xserve -- have generally been more expensive than the consumer line, but also, in general, much more upgradable. They followed a very different design and replacement cycle philosophy. If you invested more than $10,000 in a loaded Mac Pro, you wanted to get as many years as possible out of it, and were more likely to add and upgrade the hardware over time instead of buying new, at least until there was no other option (as was eventually the case with my venerable 8500). As a result, the enterprise market and the Pro line of products has generally generated a smaller sales volume and profit, and therefore arguably has been of secondary priority for Apple. Case in point: note the lack of a major Mac Pro update in the recent product releases -- Apple says the Mac Pro is due for a more serious refresh in 2013 -- and the total disappearance of rack-mounted products (Xserve RAID and then Xserve itself) from the line-up.
As for the laptops, particularly the MacBook Pro. Apple has dropped the 17-inch model, typically a pro-sumer item. While some were fans of the big screen, it hasn't been a big seller in recent years. And the consumer-level Macbook is no more, potentially replaced by the combination of iPad and MacBook Air. So that leaves two types of currently-shipping MacBook Pros -- the 15-inch Retina MacBook Pro, and the updated "old school" 15-inch and 13-inch models. The older models still allow for relatively easily RAM and hard drive upgrades, but the new flagship is, like iOS devices, now a sealed-unit, utterly non-upgradable. Speculation is that the rest of the MacBook Pros will go in the same direction when they get Retina displays.
A troubling trend
This is a troubling trend for many professional Apple customers, who may feel that a deliberate shift away from upgradable hardware does not meet their needs. Some of the changes point to the fact that laptops are in many ways a special case: the desire for ever thinner, lighter portable machines coupled with the need for more power, drives the decision to fill every available space in the smaller cases. The result: non-upgradeable hardware.
Case in point: batteries. The one essential accessory with every Mac laptop I've bought used to be a spare battery or two, so I could swap them out on long flights and extend my time away from an outlet. When Apple switched to internal, non-swappable batteries, it boosted battery life by cramming more capacity into the chassis, but took away the ability to switch out batteries. This is a calculated trade-off, and for many users, having a bit more battery life built-in may be more important than swapping. The other, less obvious consequence is that when the battery starts losing capacity and finally fails (as all batteries eventually do), replacing it with a new one isn't a simple matter of buying one and dropping it inch
If you want to replace it yourself, you have to crack the case (potentially voiding any warranty you may have), and do what can amount to major surgery. Apple does offer an out-of-warranty battery replacement service at a reasonable charge ($129 for the MacBook Air and most MacBook Pros, $199 for the new Retina Pro), but if a user decides to replace a Retina MacBook Pro's battery, and does it according to Apple specs, iFixit estimates a $500 cost -- ouch!