I don't know if I believe that. My wife's Yukon has an automatic 4wd transfer case and it definitely gets worse mileage when it is engaged than when it is not engaged.
I don't think this is what you were suggesting, but a transfer case that does not allow slippage between the front and rear axles would not be suitable for full time use.
The Constitution needs to be re-read, not re-written!
If you can't handle Dr. Seuss, how will you handle real life?
Current oil burners: MB GLK250 BlueTEC, John Deere X758
New ride: MB GLS450 - most stately
Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510