In a coolish environment (under 80ºF and no direct sunlight) metal tends to feel cool. It's a good conductor of heat and draws the heat out of your fingers; making it feel cool, even though it's at or near room temp. Plastic on the other hand does not conduct heat well, and tends to feel more neutral at room temperatures.
The iPad being cool enough to feel cool is good. It means it doesn't' have a heat dissipation problem. On the other hand, if you play a graphics intense game for a while I believe you'll find it makes a nice hand warmer. If it does not, then it will be the first iPad not to warm up at least a bit under heavy load.
Most Android tablets also warm up nicely with heavy use.