I don't really equate Kate's life as being the same as Moshpit, at least Kate has known her beau Wills since University days and she
was there on her own credentials, yes she is a well taken care of type, by means of her parents and connections of the wealthy jet-set (ie jobs), but Mosh is not in the same league at all. Kate is no blue-blood, but she's been hanging in these circles her whole life - Mosh was a cheeseball, struggling to place herself it in all the right neighborhoods with roomies and skipping from job to job trying to make connections with the "right" folks.
The Royal family ordering her out of the race is puzzling to me if we are supposed to believe that Wills and Kate are no longer a couple (I for one never believed in the break-up) what right would they have to give her orders in anything if she is nonentity in the family. Also the fear of papparazzi storming the race
now I would think media attention at a charity event would be terrific, raising all sorts of mega awareness to the cause (if not for the wrong reasons of following Kate). The royals probably got wind of the topless thing prior and panicked more about that than they did the boat race media storm.
As far as clubbing, she's doing what every "social circuit privileged 20 something" is doing, I dare you to enter any club in Knightsbridge and find anything but, just so happens she's dated the future King and is in the spotlight. She's a party girl, but hell so is Wills and Harry - it's what they do for nightlife fun at this stage.