Was than an argeement or sarcasm?
In each step up of terms, there is 2^10 of that unit. So 1 gigabyte is 2^10 megabytes = 1024 megabytes. This is because computer systems are based on binary and not decimal. Whether or not harddrive manufactors and so on listen to this fact is a different matter. That is why harddrives often have less "real" space on them than what is advertised. This is because the companies often advertise them with 1000 units needed for each step (ie 1gb is 1000mb) instead of 1024 units. The uneducated user is then suprised to find his 80gb harddrive, in Windows, is not quite so big.
I have never heard of this ambiguousity with RAM, though, but unless the poster enlightens us with more information about what "exactly 2 gigabytes, no 2048mb, go figure" means, I cannot say much more. Since all RAM is sized using the binary system and not decimal, you would be very hard-pressed to find a stick of 1000/2000mb instead of 1024/2048mb, so I don't use how you could have exactly 2 gigabytes, but not 2048mb.