Your example is not a very good one.
"Graphics ram and system ram are both measured in MB and GB, but they are not interchangeable."
MB, GB, Mhz, etc are all units of measure. They have nothing to do with components of a computer.
Your example is like saying I need 1 qt of brake fluid can be confused with 4 qt's of oil. 2 totally different things, but the same unit of measure.
You would have been better off with comparing something like DDR vs. DDR2 or IDE vs. SATA.