you're confused

the real name of an operating system is a "mac osx" and the version number of it is "3.4" currently. it is written "10.3.4" simply because the sorting order is easier to manage that way. "X.3.4" would be just as correct, but instead of listing the version as a first one, the x-wrinting style puts it to the bottom.
so to repeat myself: we have a mac osx 3.4 currently, not a 10.3.4 or ten-whatever. "10" equals "X" and that just means "OS X" - a new generation of macintosh system.
the version number (3.4) is a combination of "major" and "minor" version numbers and is NOT a binary number. so there can very well be a mac osx 999.999 if steve some day wants so. these are two integers combined together with a period. not a binary.