I have some experience with GCC releases -- having served as a GCC
Release Manager for several years. In fact, the release scheme we currently
have has gone through several iterations -- usually after many "existential"
crisis. Yes, we don't break GCC ABI lightly, mostly because GCC isn't
a research compiler and most "research works" are done on forgotten branches
that nobody cares about anymore. Implementing new standards (e.g. moving
from C++03 to C++11 that has several mandated API and ABI breakage) is a
royal pain that isn't worth replicating in GHC -- at least if you want
GHC to remain a research compiler.

Concerning your question about release number, I would venture that there
is a certain "marketing" aspect to it. I can tell you that we, the
GCC community,
are very poor at that -- otherwise, we would have been at version 26
or something :-)

Thanks for sharing! My perspective is of course as a user. I don't think I've ever run into a case where the compiler broken a previous work e.g. C++ program. On the other hand I have to make a release of most of the libraries I maintain with every GHC release (to bump cabal version constraints to accept the new base version, if nothing else).

-- Johan