I think the biggest issue: there's more money behind "successful" US series compared to "successful" British. When a show gets big, more money is dumped on it.

I think the biggest issue: there's more money behind "successful" US series compared to "successful" British. When a show gets big, more money is dumped on it. The issue with that goes beyond the standard creative problems that occur, it's also the management. When a show starts having budgets in the millions upon millions per episode, there are more eyes and thus, voices involved in the process that originally ignored said show when it was a "nobody". Eyes and voices that any logical person knows should be blind folded and gagged from having any sort of creative to artistic opinion. But, because their signatures are on the cheques, their word becomes law. From what I understand (please correct me if I'm wrong), that doesn't happen all that much with British shows as there's such a finite overall production budget and personnel to that market demographic compared to the US. There's budget increases to good shows, but it's no where near as drastic as what may happen to an American one.