Here's the way I see it:
Memory is memory is memory.
However...
As with most manfacturing processes, there is a certain percentage of flaws, errors, and other minor problems that can show themselves. Since memory (and other electronic components) have a very low tolerance for error, these can be the cause of bad ram.
The only difference I see in so called "generic" ram vs. name brand ram (like Crucial) is that the name brand stuff is usually more throughly tested before it leaves the plant. This is one reason why they can say (and for the most part true) that their ram is better.
That being said, some OEMs actually buy their ram from a good company, just with out the name. And I've heard that in some cases, the ram that's tested that not 100% good can in some cases be sold to OEMs.
Take all this with a grain of salt though, as this is not, in anyway, official. Rumors, hearsay, etc are very common in this type of thing. So don't flame me.
Last point: As with any product (from clothes to computers) you're paying for a name. Name brand recognition is a factor as well.
-Ryandor