This is very much a YMMV situation. Whether demand is sustained or not, I don't think it's ever that unexpected for new gadgets like this to sell out just because there's always going to be an audience that wants the latest and greatest thing on day one. I mentioned this not too long ago, but I want to again reiterate that for about 2 - 4 weeks, the Wii U appeared to be selling out in many locations, and it wasn't just due to artificial scarcity as the console was breaking previous sales records.
As someone who's never preordered a console and has owned every console day one, not worried. I'll be able to walk into any store and grab it day one. Just like with every console in history.
With new tech I think there's a couple of factors. One is just that it takes a bit to ramp up production to mass produce a device that can meet the demand. Two is that you definitely don't want to overdo it and wind up sitting on a mountain of inventory that you can't sell.