We plan to update these binaries frequently. At least once a month. It is hard to get a good tested build across all packages we currently ship - so the preference is to not Pkg.update() and just get a new JuliaPro release. Once Pkg3 releases, we hope to be able to do this with finer granularity.
Currently, we precompile everything in order to have a good first experience. This turned out to be a non-trivial amount of work. Of course, Pkg.update() will work if you do it, but then all the usual caveats apply.
A lot of moving parts for now, but we figured that the best starting point is to put everything together in a single installer and release on a regular basis. As Pkg3 releases, we can include many more things and also have finer granularity of what is installed.