It's a common thing in language standards to version by the year the standard was ratified, especially for ANSI languages such as C and C++, but there's a long history of it in language design including the ur-example off the top of my head of ALGOL68.
As for Windows 98. Would you seriously with a straight face want to admit to using a version of Windows that is old enough to vote? If anything, it's too bad they stopped that pattern with XP as it would have been a lot easier to shame people for still using Windows 2001 in 2015.
So yes, this certainly feeds my point that standards years can be useful to point out the quirky failings of software by potentially adding to their shame. It's 2016, are you using an SQL-1986-compliant database?
So it's not that standards become out of date, especially as in both Javascript and C++'s case, the standards are generally additive. They just add stuff so your old software should continue to work and will not become "out of date".
Anyway, that's the reasoning I've been given behind the change and it makes sense to me. Hopefully that answers the question for you as well.
C++03
C++11
C++14
C++17
Ubuntu?
16.04
13.10
9.04
If the end digit had matched, I suspect it would have worked out better, but with ES2015 and ES6 being equivalent, it's pretty confusing.