Frankly, I think if members are stupid enough to pay for something week in, week out, without putting any thought or effort into it themselves, then they're fair game, in exactly the same way as gym members who turn up once a month.
I'm actually a WW online member for free at the moment, having signed up through a cashback website and opted for the reduced three month membership. I'm doing really well (hoping for 7lbs by Thursday, which has taken 4 weeks). I don't eat any ready made stuff, and no ww products, but I do have a bit of normal chocolate and eat biscuits as part of a balanced diet.
This is my second successful go at ww, having lost 2 1/2 stones before TTC. I personally opted to throw healthy eating out of the window during my pregnancies as I'm a greedy bastard.
That said, I have tried ww at other times and been unsuccessful (see my point about being a greedy bastard). That was simply because I wasn't committed to following the plan fully. I just stopped turning up to meetings and therefore paid nothing. Nobody held a gun to my head and marched me to the cashpoint for next week's subs.
Whether or not Weight Watchers works is down to the individual. It does for me because it helps me to put a limit on my less healthy habits. If you wanted to completely detox your diet (I don't) or want to take a low carb approach (again, I don't), I can see that it wouldn't be ideal. I just want to curb my normal eating habits without changing them. It's up to me to have the self control to stick to my points. Much easier than farting about counting calories, carbs or.whatever for me.