It is an old an tired argument about the differences between the US IR and the CAA/JAA equivalent.
Although the FAA IR does require lower flying standards than the JAA equivalent (check out the ILS deviation allowed in the FAA PTS) I don't think that it is sufficiently different to prevent the CAA from endorsing it over.
I suspect that they don't really want to encourage lots of tiny aircraft into controlled airspace...but I may be wrong.
2D