"every worthy, able young man should PREPARE to serve a mission." The next line says, "missionary service is a priesthood duty." If we want to overanalyze this - and isn't that what CB is for?- there's nowhere in there that says every young man should serve a 2-year mission.

Preparing for a mission is not serving a mission.
If every young man (and woman for that matter) lived their life as though preparing for a mission, they would be great representatives of the church no matter whether they served a "standard" mission or not.

Missionary service can cover a broad range of topics.
Jimmer in China right now is a great example. I think he is making a much bigger difference by utilizing his unique skill set to reach many more people than he could have ever done by going door to door.

I think Joseph Smith said it best, "We teach correct principles and allow the people to govern themselves." (might not be an exact quote, but I think that's about right).