I'm not so sure that its about money, the Neo 09 event here in the UK back in April (1/8th buggy) attracted a lot of top US drivers, as well as other nationalities.
In fact, heres the numbers:
Austria (4), Belgium (2), Brazil (1), Czech Republic (3), Finland (1), France (13), Germany (9), Greece (6), Indonesia (1), Ireland (1), Italy (2), Japan (1), Malta (2), N.Ireland (1), Norway (8), Portugal (8), Slovakia (2), Spain (7), Sweden (7), Switzerland (1), UK (86), USA (11) and Wales (3).
Interestingly, I found this question/answer in an interview with Jared Tebo at the Neo 09 (via the oOple.com site):
oOple - We hear you'll be defending your title at the 10th Worlds in South Africa later this year - how do you think you'll perform with the underdog Kyosho?
Jared Tebo - Uhm, if the race actually happens I think it will be pretty good - I like my cars a lot, I don't think I'm at any disadvantage or anything like that. I can't believe it is in South Africa.