4) The Vong.. I was thinking about the very thing you brought up.. When Obi-Wan says "The Force surrounds us, It penetrates us, it binds the galaxy together.".. but to add to that.. Qui Gon says "Midi-Chlorians are a microscopic life form that resides in all living cells" and even says "Without the Midi-Chlorians,life could not excist". It's like the writer never even watched the movies.
I Thought the Easiest/Best Explanation for it was Because they Come from another Galaxy, they have a "Foriegn Language" Version of the Force... Plus the Fact they Were cut off from it.
That said the Idea of it was interesting. Even if they Were still connected to it, it may have been Difficult for the Jedi to sense them.
I'm Probally wrong but we'll not likly know.