EPSON C84 & C64 Printing cost comparison

I've been searching around the net for a new printer and I found something peculiar and also rather rediculously odd about the printing capacity between the EPSON C64 and C84 Printer. From what I can tell They use exactly the same set of ink cartridge, they have the same drop sizes. they are supposed to print the same quality if they have the same amount of memory buffer even with different amount of nozzles they should produce the same results it's only the matter how long it takes to produce it. so I did call EPSON, and they said they should produce the same result and they don't seem to understand why it has different capacity either. So assume that the printing quality are the same. and the only conclusion I have is EPSON cheated with the cartridge. in order to make people believe c64 printing cost is more. they programed the c64 to believe that there are only so much amount of ink in the cartridge (remember the cartridge actually have its own memory circuit). which also means, according to THG that C64 will produce more unused ink than C84, but these are all my speculation. i hope anyone can tell me the truth.