This is more a question of address space. If I have 1 bit, I can address 2 things (0, 1). If I have 2 bits, I can address 4 things (00, 01, 10, 11). With 2 bits

This is more a question of address space. If I have 1 bit, I can address 2 things (0, 1). If I have 2 bits, I can address 4 things (00, 01, 10, 11). With 2 bits, you can also address 3 things, but then you are wasting precious bits, so it makes sense to try to fill up the address space available. Basically everything inside a computer is based in binary and is therefore held to some relationship with powers of 2. The way these addresses work in hardware is basically to go into a massive decoder that lights up the right bit and makes that bit available. If you don't use all your bits, you are basically wasting available logic circuitry. In most DRAM (which is what you think of usually talking about RAM), the capacitor is not the expensive part, the control circuits are, so if you waste control circuits, you are not making the best performance/cost proposition.