I always liked the Winamp approach: ship a core system with a base set of plugins, and implement new functionality via new plugins. The base system almost never

I always liked the Winamp approach: ship a core system with a base set of plugins, and implement new functionality via new plugins. The base system almost never changes, and version updates are simply a new payload of plugins. Why do the best plugins need to be added back to base? Why not just keep them separate. Believe it or not Firefox was originally written in this fashion, but right around the time they added built-in spellcheck, new functionality started appearing as additions to the base system as opposed to browser extensions. Why?