If you add a washer or two under the two steering stop bolts, you can run 4.5" of backspacing on a TJ with 33x12.50 and 35x12.50 tires. I did it for several years and it was perfect. You were talking to a sales-droid who probably drives a 2wd Toyota p/u truck jacked up to look like a prerunner who knows nothing about Jeeps.
I preferred 4.5" of BS because it kept the tires tucked in more which was better for the narrow types of trails I seemed to be finding myself in.
To be sure, 4.5" of backspacing is the most backspacing you can safely run with a 12.5" wide tire. Go to http://www.imajeep.com/Steering_Stop...ering_stop.htm
for directions on how to add the washer (maybe two) under both steering stop bolts. Doing so will VERY slightly increase your turning radius but I sure never noticed it myself... it still turns on a dime.