Сабж. Оно всё это время было в Changelog'е. Как оказалось, вычищают не совсем все .la файлы, а только в LD_LIBRARY_PATH (/lib{,64} , /usr/lib{,64}).
Причина - массовая миграция софта с autotools на другие сборочные системы, которые не генерируют .la файлы, и это может привести к проблемам с зависимостями если вовремя не избавиться от этих .la файлов.
Актуальный кусок текста от Патрика:
One of the reasons that this really needed to happen is that many projects are starting to migrate to build systems other than autotools, and those systems do not generate .la files. So if we didn't get rid of them now, we might end up in a situation later on where they are being removed by upstream and then we would have to chase down the dependency breakage and recompile (possibly many) other packages. The .la files that are outside of the LD_LIBRARY_PATH were not removed (and shouldn't be) - those ones are often used by the lt_dlopen() function to load plugins and removing those ones can break things. But those ones don't cause problems... they aren't likely to try to infect .la files produced by other packages.
