Yeah, at 600MB/s, 50 seconds of loading is 15GB... So ok, it can't fill my RAM at HDD speeds, but no, none of those use anything near 15GB of memory at startup. (If they did, my question would be WTF are they doing with gigabytes of memory.) And well, loading from disk ought to be the bottleneck of any reasonable cache.
About pre-computing things (that's very likely the answer), the question is what things? Excluding Visual Studio, those are very plain GUI programs, that have a huge amount of options, but not anything near enough. And on the Visual Studio case, all the indexes and intelligence helpers are certainly cached to disk, as it's impossible to recalculate them at load time (the information just isn't there).
One thing those 3 have in common is that they have complete language emulation environments that are exposed to the user but are not related to their main function. Yet, language emulation environments start-up much faster than that, so they can only explain a small part of that time.
