When a library changes, the packages the depend on it often need to be recompiled. Hence the bin-nmu. Though this automagic goodness for Release Managers is a fairly recent innovation.
16:01 < hendry> i don't quite understand 16:01 < hendry> how can it just be a change to the changelog 16:02 < hendry> is this just to hack, because Katie won't retrieve same source upgrades 16:03 < pabs> no, its just so that the version is higher in the new .deb 16:05 < pabs> example changelog entry: http://paste.debian.net/8186 16:08 < pabs> and katie is no longer named katie 16:09 < pabs> you can find a list of binNMUed packages with aptitude search '~V\+b[0-9]+$' 16:12 < pabs> basically it is a way for the release managers to simply recompile packages when that is nessecary. like if a library moves to a new soname, the packages depending on it can be binNMUed 16:48 < adsb-work> Technically it's a recompile with no source changes, hence a binary NMU