Well.. I did 12,000 miles in my LJ this summer, probably about 3000 or so off pavement. They way I had things packed changed entirely from the way it was when I left. I ended up with essential supplies and spare parts in the Jeep with me. That consisted of... Some food, Plenty of water, the engles, recovery gear, first aid, Spare Axles, Driveshafts, Unit bearings, Ujoints, and tools there was also a small ground tent and my sleeping bag. Everything else stayed in the trailer. Main food supply, cooking supplies, clothing, genorator, Overland tent, Mountain bike, Bulky items etc.
The rig itself is equipped with On board air, Hot water shower, dual batteries, 2 engle fridges, snorkel, lockers front and rear, 35" tires, Long arm suspension, Wilderness Rack on the back (Which never made a peep the entire trip.) I was on the road for 3 months give or take. I had to stop for food supplies every 2 weeks or so. The rig got me everywhere I could have wanted to go and alot of those places pulling a trailer. The only real breakage I encountered was a wrecked factory rubicon locker in moab. The only thing I would do differently would be to run some sort of all terrain tires because I did spend a lot of time on highways and the hum started to get to me after a while. (Nothin earplugs and a good stereo couldn't fix :rockon: ) also the Thule bike rack I use was never designed to go 40 mph down a washboard road and that became apparent early on in the trip. It never failed completely but that mountain bike sure did swing around a lot! Otherwise I was absolutely thrilled with the performance of the whole setup.
Now for fuel capacity... We are in America! There is a gas station at least every 100 miles. A few times, poor planning on my part left me on the side of a dirt road using one of my Jerry cans, but for the most part the only time I REALLY needed extra fuel capacity was when I ran the White rim road while pulling a trailer. I put every drop of extra fuel I had with me in the main tank and I still had 1/4 tank left when I got to the fill station just outside of canyon lands NP. If I were thinking of going to the outback or run the paris Dakkar, or even some of the more remote places in Canada. I would tend to agree with you about range. But here in the lower 48 I don't think it is as much of a concern.
Now that I am back on the east cost there really isn't any wide open space like out west. Mostly it is off-road parks and such so I have made some further modifications to the rig that really have diminished it's street ability, but has opened new doors as to where I can go with my rig. And I recently acquired an old Comanche to fill that expedition void. I will be building that up over the next year or so to run another similar trip down the road.
So to answer your question, I think that an LJ and even a TJ with expert packing skills can be a very capable expedition vehicle. Sure there is other vehicles out there that would be better suited to the task but they are lacking in other places. For me I wouldn't have any other vehicle than a Jeep (Maybe a Uni-Mog). The whole time leading up to this trip I had it in mind to really make an all purpose vehicle, and I think it was a great success.