Apple must have a guaranteed supply of memory which meets their specs (speed, quality, package type, etc.) and in huge volume. An aftermarket supplier is typically under no such constraints. That said, it is no doubt a high profit margin option for them. If you think that is ridiculous, consider the machine tool industry where a floppy drive (the same one you can buy for $25) sells for $500, or 256M of memory might be $1K or $2K. Because they can.

Battery doors are another matter. That takes very significant space and thickness in a product category differentiated by those specs. Not to mention the warrantee returns it causes. According to Larry most people won't open the case to change the battery - in fact most people would not have a spare battery and replace it even if it was available. You might think having it be 2 mm thicker and have a replaceable battery is the right tradeoff, 95% of the customers don't think so.

I'm not judging who is right or wrong here - just telling you what goes into the decisions.