Here's the way I see it:
Memory is memory is memory.
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.
the CAS latency can be lower on branded ram than on generic ram. Ive found crucials ram is usually CAS latency 2, whereas the majority of generic ram tend to have a CAS latency of 3 (the lower the better).
Sometimes you see an improvement in access speed to the RAM also... Crucial have notes next to the RAM on their website which tells you the access speed (they refer to it as 'ns' i think) and the CAS latency (they use CL).
So there is a difference. You can make CL3 ram run at CL2, but its like overclocking and may cause damage to the ram/motherboard over time.
This would be a perfect example (at least to me) of the "ram that's tested that [is] not 100% good."
There's no way to know the percentage of ram is not 100%, but why wouldn't a company (not necessarily Crucial) take that stick of ram that, when tested, wasn't "stable" at CAS latency of 2, and sell it to an OEM company as a "CAS latency 3" product?
It would make perfect sence to me. Why throw away a borderline product that works at lower speeds when you can at least recoup some otherwise lost profit?
surely that means the term generic is the common ground - i.e. it'll work on everything? Branded tends to mean companies can charge more for it. They probably sell stuff that wont run at CL2 as CL3 goods at cheaper prices intending for people who cant afford the normal price to buy at least some ram at the cheaper price.
to be perfectly honest though, CL3 can make a real speed impact compared to CL2. I used to run a system with the ram as CL2 but it was really CL3. Didnt have any problems or anything... just decided to go back to CL3 and I noticed things took longer to finish etc when using ram. but that may not always be the case.