Americans in the middle class and above aren't strangers to spending substantial amounts of money on stuff that they don't need. Segways are useful enough that I could imagine them gaining a substantial market share if it were fashionable to use one.
Now, that doesn't mean that they would catch on if they weren't dorky. But even at the outrageous price that they were marketed at, I think it's conceivable that they could -- I think they'd have similar chances to other potential fashions. So I actually think I agree with PG more than you. Price and insubstantial benefit are both major problems with the Segway (and frankly I'm being a little devil's advocate here, the price was ridiculous -- but cut it in half or so and I think it stops being prohibitive), but the aspect of Segway that made it impossible for the thing to succeed was its dorkiness.