OK... so it appears that the majority believe there is a difference, even if it is just a subtle difference...
That leads me to ask a few more questions then...
1) Why do high-end restaurants, that can afford the best of "setups", grill over gas?
Efficiency, ease of operation, less training, cheaper.
2) I have done my fair share of charcoal grilling over the years... and I get just as many "this food is great" comments whether I cook on gas or charcoal... in fact my last steak cook was done over gas, and was probably some of the best tasting steak I have ever done.
3) When grilling w/ high heat... it seems everyone claims they can taste a touch of smoke... I don't think that smokey taste if coming from fuel source, but rather fat dripping?? Not sure, but I think. If I am correct, I get the SAME smoky taste using Grill Grates on my Genesis.
You are correct in that most of the "smoky flavor" in a steak cooked over either gas or charcoal comes from the juices/fat dripping out and hitting the burner or coals, then smoking up. I can tell a major difference in flavor between cooking over wood, but not so much with charcoal. Charcoal briquettes have a nasty, acrid odor and flavor when first lit, but add pretty much no flavor at all after they've turned white. They're a clean source of heat, just like gas. Again, all the "smoky" taste cooking over briquettes comes from dripping fat hitting the coals. Lump charcoal is made from wood, and has some flavor of its own, enough to tell a difference. Actual hardwood coals from burning down wood add a lot of flavor to what ever you're cooking. To me, pretty much no difference in taste between gas and briquettes unless you throw some wood chunks on the briquettes for smoke. A noticable difference between gas and lump, and a big difference in taste between gas and wood.