I've taken the liberty of editing your first sentence, davie, simply because, before this year, I'd have agreed with it completely, even I though I have two friends who've lived together for 6 years and got married a year ago, despite/because* having met as WG/client. Again I'd totally have agreed with the rest of your post, until earlier this year.
However, as I've posted on other threads, I've "blurred boundaries"/suffered Emotional Attachment Syndrome *. And once that's happened, it's difficult to return to the first rules of Punting Club, despite your big brain telling you to do so!
* Delete as appropriate.
I can understand what you're saying but I can only speak for myself and my own situation. No matter how close I have been to a WG, in my case anything other than a client / provider relationship is just not going to happen. The main reason for this is I'm happy being single and do not want a relationship. Of course the age gap would play a part as well!!
Being a bit on the older side I do tend to use the same WGs who are genuinely happy with my age, hence more visits to the same girls and getting to know them more, all leading to better punts.
I suppose if I was younger I might mistake any 'affection' shown by a girl to a client in the course of her job for something more so each to his own I suppose.