I think the doc patch should mention that:
 1) it's 'linux2' also on Linux 3;
 2) why it's not 'linux3';
The why can be done in a footnote and explain that Linux 3 doesn't introduce new major features and that changing the string to 'linux3' would have just broken needlessly code that was checking for sys.platform == 'linux2'.
It should probably also mention that in future versions (i.e. 3.3+) this string has been changed to be just 'linux' and that keep checking for sys.platform == 'linux2' is therefore discouraged even after this change.