I honestly believe that most of the casual riders don't really benefit from the shorts in any real way.
At the pro/serious level; you want ever advantage - and bicycling shorts give you a (small) advantage. But people emulate pros and spend a lot of money on things they don't need.
a co-worker of mine just started riding and was asking some of the more knowledgeable (but all, very much amateur) riders for advice on a road bicycle. They were looking at two bicycles; side-by-side. One was about $300 dollars cheaper and weight 22.8 pounds, the more expensive one weighed 19.something. "Yeah, I dunno man, 22.8 is pretty heavy for a road bike".
The bicycle was for a guy who had to be, at least, 20 pounds overweight. He'd be riding into work with spare tube, tools, hand pump, water, his work clothes, dress shoes, etc...but he really thought it was a good idea to pay $300 dollars more to essentially reduce the weight of the bicycle by 3-4 pounds.
I'm guessing he's 180 lbs + everything he'll carry = 190. Plus the weight of the bicycle (either 19 or 23) and you get 109-113 pounds. A complete newbie to riding just paid $300 dollars because he wanted to reduce his riding weight by 3%.
I feel like bicycle shorts are the same. If you are comfortable with what you've got that's what matters for 90% of all bicycle riders. If you are concerned about being able to ride as far or as fast; or if you've tried them and simply prefer bicycle shorts - then sure, pay the extra money for them.
They aren't needed, but there is a point to them.
EDIT: God - I'm retarded this morning. The total weight should be between 209 and 213. The weight reduction should be 1.8%