^I accept the example cited, so my theory might sincerely be in error. However, name a primetime successful science fiction show, on one of the major broadcast networks, that Doctor Who would actually work on.
NBC? Hardly. Not unless it has something to do with Law & Order, or can tie into The Office.
ABC? Only if they could redo it completely and call it LOST II.
CBS? Well, the elderly might be more open to it. But, I'm pretty certain the accents would throw them off immediately.
FOX? They had their shot...
So, while I agree that a mutual reason US audiences wouldn't be into Doctor Who is because of how cut-off generations have been from foreign television shows, I would also find it very hard to swallow that a majority would get into any lead character as "un-macho" as The Doctor. About the time he talked his way out of a situation, and the Dalek hasn't just shot him in meantime, the majority would probably tune out.
Now, all of this is based on past experience, versus the broader open minds of the 21st century and future citizens. But, I'm still pretty certain, without a network's primary support and backing, a marketing craze that finds a popular niche, The Doctor adopting an offensive-styled weapon, and an American "doorway" character, Doctor Who would be doomed on primetime US airwaves....