Peter: For one thing higher ratio's of FAs to Passengers in Premium cabins mean the FAs have more time to be attentive.
Another is they have more goodies to be attentive with.
And finally, some cabin crew are good in First/Business and some are good in Economy. The airlines know this and allocate the crew where there talents are best served.
As an example if a FA is serving lunch in Economy, she gets to the passenger in front of you and he asks for a copy of the Herald Tribune and she 'nicely' offers to go fetch one from way-back straight away are you going to be happy that you were kept waiting? In First they have the time to give individual attention and they build the cabin timetable around you rather than the other way round.
Nick