This is all purely from dodgy memory recall, but I think the situation is:

* in terms of UK record sales they have outsold Top 40 records on a number of occasions but don't qualify due to some strange rules that we have regarding music genres - they are classified as religious music and thus don't qualify for pop chart possitions

* the BBC won't give them airtime as they cannot find bands for other religions to balance things out (needed because of the BBC's impartiality rules)

* tickets for their Wembley Stadium concert sold out

* they have sold more albums in the US than Robbie Williams

* the US is now a more lucrative market for them than the UK

* the US rules on genres and chart positions are different

...as I said - from memory.