This is an interesting solution, because the problem is that the original codebase is messy and therefore not portable. It seems to happen to most software as it ages.
Putting it on a server makes the architecture more robust against messy code (and changes in programming languages and environments), because pieces can be changed independently.
The problem isn't that the original codebase is messy (it's aged, but there are still comparatively new projects working on it e.g. LuaTeX) or that it's non-portable, as demonstrated by the multitude of platforms it's available for.
The problem is roughly equivalent to producing a non-upgradable perl. It's not very useful on its own, but it's completely impractical to include a copy of the entire CPAN with it. And Apple's policies prevent you from downloading additional packages. It's just not worth the effort.
Putting it on a server makes the architecture more robust against messy code (and changes in programming languages and environments), because pieces can be changed independently.