Indeed we have. I am sick of the silly excuses big developers use for not making a demo. They even try and tell their own programmers its for some fuzzy reason, yet we all know its because they expect to sell the game based on hype.
How about taking 10% of the marketing budget, and using that to make a kick-ass specially designed demo that lets you experience how cool the game really is?
That makes more sense to me, assuming you know you have made a good, fun agme and not just a hyped tech demo.