(I design memory controllers ....) you can sort of do that depending on where your byte boundaries are (and whether your architecture needs to be able to do single byte writes to memory) - more though I was trying to point out that historically just 'burning some bits' was not something you could practically do cost wise (it's why we built a 9/72/81-bit CPU in the 90s rather than a 16/125/128 one - the system cost of effectively doubling the memory size would not have made sense)

These days (and actually in those days too) memory isn't really the size of the memory bus, often it's a power of two multiple - those 9-bit RAMBUS drams we were using really moved data on both edges of a faster clock - our basic memory transfer unit was 8 clock edges x 9 == 72 bits per core clock - as a designer with even 1 DRAM out there that's the minimal amount you can deal with and you'd best design to make the most of it