|First of all, you should note that there's a difference in price. Just check prices for memory, and you'll see that the higher density ram costs more. If you settle for what the company wants to give you, then you'll be losing money. The company is only looking at quantity and not quality.|
Second, some motherboards only have 2 or 3 memory slots (ie: micro ATX mobos). Maybe pretend that you don't have 4 slots?
Also memory slots do go bad sometimes. One of mine went bad. If I had 4 memory modules, then I would have been screwed.
For performance reasons, it's better to go with lower density ram if possible (in dual-channel configuration, it might not make a difference). That's because the computer uses the first ram chip until it's full, then it uses the 2nd. If you had lower-density ram, the first one would fill up quicker, so your computer would be using the 1st and 2nd ram at the same time. Thus, you wouldn't have to wait for each previous memory operation to complete. (It's been a couple of years since I had my operating systems class, but that's the gist of what I remember).
You should get what you paid for. If they don't make it anymore, and want to settle for something cheaper, then you should get some sort of compensation. I'm sure if you wanted lower-density ram, you would have bought it. Graphic-intensive programs need alot of ram, so perhaps you were leaving two memory slots open for future upgradeability.