The essence of Dispensationalism is recognizing the difference between the church and Israel.
Thus my objection to the faulty poll listed in #481. Various assorted rapturists were listed as dispensationalists, including post-tribbers.
They arrive at that conclusion biblically, and it is based, if I remember correctly, on the sequence of events and persons present at the time of Jesus' return. I had a good friend, a Conservative Baptist, who was solidly post-trib, and very skilled in explaining it biblically.
My concern with it is based more on who inhabits the land after the return of Christ, than it is on whether or not Christians suffer persecution in the tribulation. One can make a number of points about Christians and tribulation and about Christians being protected but present.