My 4.0 has 212,497 on the clock right now, and still runs like a clock. Bone cold weather, even into the negatives, starts right up first crank. Its had a heck of a rough life too... it gets the dog sh*t run out of it.
Its quite possible to see these motors last for a very very long time, especially if you keep up on oil changes, etc. Just the basic stuff that every motor needs.