Merging 1.9.7.0 and 1.9.2.7-7f-pre7

I wonder what are the differences between 1.9.7.0 and 1.9.2.7-7f-pre7.
I am a programmer but I am not familiar with linux.
I am considering trying to compare the sources.
Any advices?
How come Oleg knows to improve the firmware?
Are there on the net any learning resources
relevant for Asus router?

The sources are different. Merging the stuff is a pain...

I see. Indeed your firmare is much slimmer so it
should be very different