Some of apples products have RAM directly soldered to the motherboard. This has legitimate engineering trade-offs. Of the ones that don't do this: Are there any that deliberately void compatibility with alternatives. It looks like most of their cables have alternatives too. Their stuff is expensive sure. But are they deliberately locking you into using their accessories?
Heard of damning with faint praise? I'd say this amounts to praising with faint damn.
Given that their devices cost less, I can forgive them the convenience cost of an in-store RAM upgrade when they're helping my Mom upgrade RAM or HDD in her beloved 15" Macbook from years ago that still works a treat. Most customers are not really the NewEgg type.
To grandparent's point about costs of low turnover stock, these parts cost more for much better reasons than Jiffy Lube oil costs more, yet most people prefer Jiffy Lube except mechanics or DIYers.
Perhaps this is true in America but I'm pretty sure it's not in many other places. I recently looked around for a laptop to put Windows7 on and while it was discouraging to see the quality of the laptops that were available (compared, not just to a MacBook but to other laptops that existed 3 years ago) they were significantly cheaper and higher spec'd than a MacBook.
Similar to the external hard drive market, anything labeled "apple compatible" costs extra, but is basically the same thing.
Find the RAM you machine needs, and search for that directly on Newegg or similar.
How to find what RAM you need: (on OSX Lion)
1. Click the Apple (top left corner of your screen)
2. Click "About this Mac"
3. Click "More Info..."
4. Click the "Memory" tab
Note: there are memory upgrade instructions in this window as well :)