Initially I was only frustrated that I couldn't get the Lumia 920 on Verizon since I am not willing to change carriers, but the Lumia 920 being exclusive will completely eliminate the chances that it will have good US penetration.
The HTC Windows Phone 8X is almost guaranteed to sell more units than the Lumia 920 in the US simply because it is being offered on multiple carriers. In fact I will probably end up buying the 8X even though I hate how it only has 16 GB of internal storage with no option for an SD card which is really the only thing that irritates me about the phone.
There is no way a phone can truly compete with the Iphone and now Samsung's GSIII as long as it is being offered on only one carrier. Many Galaxy S IIIs are being sold and is offered on multiple carriers, the One X sales and Lumia 900 sales were lackluster and both of those phones are great (Lumia was a bit outdated hardware wise) but only available on AT&T.
I know we have to wait for more information regarding the 920 being available on other US carriers (some people say after the holidays the Lumia 920 will not be exclusive to AT&T anymore) but as of right now, I don't like the direction things are heading. It would be annoying if I get impatient, buy the 8X in November, and then have the Lumia 920 come to Verizon in January. Ahh!