I've "never needed" 4wd in my truck, but my yard gets pretty soggy in the rainy season and I've made the mistake of trying to turn the truck & trailer around in the yard before, getting it stuck in the mud.

I wound up having to wait until the wife got home and we used her Honda Element to pull my 7.3 and 24' enclosed out of the mud! That was 6 months ago and there are still ruts in the yard.

Anyway, if the truck is only going to be used for towing, I agree- 4wd is overkill. less gas mileage, more parts to break, etc etc.
If you're going to be using the truck for other stuff too, then the decision should weigh more on that. since 95% of the reason I bought my truck is to tow the race car and I live on flat land, there's no need for 4wd. I just need to pay attention and make sure I don't get off my gravel drive and stick it in the mud again.