Not sure why this is so hard to understand, and there's nothing goofy about it, past or present.
Before 3.x, everything was numbered as 2.x.x. Every new "major" version of the software increased the second number instead of the first, so when they went from 2.8.x to 2.9.x (for example) in the past, that was equivalent to going from 3.x to 4.x in today's scheme. So, InoX and rmmccann, however you slice it, the 51 in 2.9.51 is clearly
a LARGER number than the 27 in 6.27. Again, not sure why this is so hard to understand.
"2.8" changed to "2.9" changed to "3" changed to "4", etc. The LAST number is the revision number, so there were obviously more revisions of RouterOS 2.9 released (51) than any other major version of RouterOS to-date.
I don't know the history of RouterOS going all the way back to 1.0, but my guess would be that they went from 1.x to 2.0 fairly quickly, but then stuck with 2.x numbering for a long time because perhaps they didn't feel like they were introducing large enough changes to justify an increase of the first number. Their thinking obviously changed when RouterOS 3 was released. Prior to that, the change from 2.7 to 2.8 to 2.9 always signified that MikroTik had upgraded the version of the Linux kernel that RouterOS was based on. Now instead of just bumping up the minor version number for kernel upgrades, they bump up the major version number. So the minor version number became the major version number, and the revision number became the minor version number.