As I wrote in another answer... ages ago, a few manufacturers made many different PCB's / modules and simply released them as the same specification memory - which technically they were.
However, these memory modules were different enough that the computer would not enable "dual channel" mode as they were not compatible with each other - if you happened to get more than one sort in a batch.
So to resolve this (mainly due to complaints), memory manufacturers released Dual channel kits. There is nothing special about these kits other than they are guaranteed to work with each other, and if your motherboard supports dual channel, so will the memory you buy.
That being said, memory seems to have become more stable in the past few years and I have not seen the rapid change of modules we used to have, so even buying individual sticks is a pretty safe bet and you should still get dual channel mode.