Bug back-porting and minor release strategy

I am not familiar with bug back-porting and minor release strategy.  Could
someone help to provide a little more detailed info? Thanks!
Currently whether a bug should be back-ported to previous release is
determined by Steering Committee or PMC member, right?  If a bug is found
in newer release, such as 2.11, but it is also exist in previous release
2.5. It would be ported to all release 2.11~2.5 separately, and it would be
specified in field "keywords", such as X.X.X_APPROVED ?
How long would usually back porting a bug to previous release.  The reason
that I ask the question is I'd like know whether the effort is deserved to
go through all bugs in new release in case the bug should be ported to
previous release while not do yet, the work/effort may benefit the quality
when the release date of my own product which ported from an older pegasus
release is very close.

Another thing that I am not very clear is what's the criterion for creating
a minor release, such as 2.9.1/2.9.2/2/10.1, and what content should be
included? Thanks!

Best Regards,
Ligong