So are you not allowed to turn the steering wheel either? The outer tires turn faster in a curve.
God forbid one tire has 5psi more air than the others (the higher pressure will make the diameter about as much larger as the new tire).
Are you allowed absolutely zero toe in angle? (Toe in makes the front tires rotate slower than the rear tires... much more so than the change in diameter of 25k miles of wear).
The full time four wheel drive system in your Jeep allows a reasonable amount of slippage between the rotation of the front axle input and the rear axle input.
This slippage is facilitated by clutches (not unlike automatic transmission clutch packs) that are bathed (and cooled) in automatic transmission fluid.
This slippage is necessary to prevent overstressing the driveline while driving on pavement, due to the things like toe in, differing tire pressures, slightly different tire diameters, etc. All the things that make the front axle turn at a very slightly different rate than the rear axle.
Quite frankly, in order to burn these clutches out, you'd have to put go-cart wheels on one axle and drive down the highway in full time 4WD.
The differing rotation caused by a tire with 25k less wear is not unlike the differing rotation it already deals with.
Measure the circumference of your 3 tires. You will be lucky if they are within an inch of each other - very lucky if they are within a half inch.
Bottom line. [b]They don't want to shave 1 tire... they want to sell you 3 tires you don't need!