You need the ".com" because mere mortals don't think about anything other than ".com". Put another way, for consumers, ".com" is assumed and ".<whatever_the_hell>" is an anti-pattern.
I've learned, like you alluded to, nearly everyone associates the internet with .com. Will we ever get past that point? I don't know. As some other comments mention, .co is not the new .com, but .co.com is.
Made me chuckle.
I gave up. Nobody understood it. They would try to add .com at the end. Every time.
http://www.amazon.com/Positioning-The-Battle-Your-Mind/dp/00...
One of the interesting ideas the author postulates is, to put it in CS terms, that people's minds work like a dictionary. Each key associates with one and only one value. And, in this case, the key is a concept, need, category, etc.
If you ask someone in the US to name a plumber they'll probably answer "RotoRooter" without hesitation. Fast food? "McDonalds". Rental car? "Enterprise". Fast car? "Corvette".
The values side of the relationship isn't necessarily uniform across a population but some keys have more uniformity than others (Fast Food).
Once a person makes that key:value association it is really, really hard to break it, if not impossible. Politics tends to work that way too.
In the case of the web, the vast majority of people make the following key:value pair association:
"internet":".com"
And that's the end of the story.