@MontereyJack,
I'm rarely duped by an American playing a Brit. I have to admit I was surprised to learn some actors weren't American born, especially ozzies like the La Paglia bothers or Alex O'Loughlin from Hawaii 5 0. I guess because so many actors have dulled their accents and so many of them are from here, the line tends to blur.
I sing. I listen to accents and voices all the time. I'm very good at mimicking sound. I can't copy my father's accent generic english accent, in fact I can't hear it, until one of my aunts speak. But I do a pretty mean norn ireland..lol
Like most people, I don't like the sound of my voice on tape, but I've been forced to listen to it. I've been complimented on my voice/accent many times. It's a very generic accent, it would be hard for most people in canada, never mind the US, to place where I'm from. I throw in a few eh! s every now and then to dispel the confusion...
I can slip into bush Albertan though, any time, and yet, I've yet to hear any actor, from any other country, ever, give any Canadian accent it's due. Sometimes it's brutal. Regardless, I give 'em kudos for trying.
My cousin works for the BBC. One of the first people she met in her career, was a voice expert. When he listened to her voice, he could pinpoint her mothers accent - birthplace, where she grew up and the area of the private school she attended, in what I would call high-school, and university. This was after she'd already had 'how to speak for radio' vocal courses.
My cousin has a very posh accent. However, since I don't live there, my perception of what an upper class accent and the local's ideal might be completely off base.
Accents aren't easy to duplicate. It takes a lot of training. Yet even then someone, somewhere will find fault. The thing is... most hollywood accents play on the caricature, because everyone gets it, the idea of Boston or Texas is enough. The very act of watching tv or acting is asking you to dispel some element of truth.
As for Niles and Stewie, I think most people know that it's a fake English accent, the kind a snob or new money might pick up. Everyone knows the accent is affected, that's part of the joke, along with talking babies and dogs. It's been a running character through American cinema since the talkies.
Even to an untrained ear, anyone who listened to Madonna speak during her
English phase could hear a fake accent a mile away.
Westerners, Americano's can hear a fake, really, we can, but we don't get bent out of shape about it. That's Entertainment.
Don't like it, don't watch.