I think that is a garbage cliche and that Brits are just as capable as anyone else of admiring others' "success" -- or, more correctly, their "financial success", since I think you are talking about wealth rather than, eg, successful relationships or successfully improving their local community or environment etc etc.
It's just that, although Brits feel very happy at the thought of wealthy people deriving happiness from the wealth that they worked for, they are more likely than Americans to balance that with a sense of social justice, ie with an acknowledgement that:
(a) many poor people also work hard and have simply lacked the good fortune (supportive family, talent, etc) to translate that into £££, or have chosen to work hard at a task that society doesn't reward with wealth, like nursing and so forth
(b) it is right, good, just for the financially successful to contribute to society in proportion to their wealth, and to do so gladly - because it is their duty in justice.
I feel super-happy for anyone richer than me - as long as they pay their taxes and don't tell lies about poverty.