There are two reasons for not providing UI in the program for all of the options in the registry:
1. The extra options stored in the registry are variously; specialised/arcane/dangerous/experimental/not-commonly-used/not-officially-supported/old/enabling-legacy-behaviour. They are not things that will be useful to the vast majority of users.
2. The Options dialog would be huge if it had to represent all this stuff and would intimidate most users. Similarly the documentation for the options would be enormous and difficult to maintain.

Phil