Leaving aside the relative skill requirements... the reason for the expense and hassle of the JAA PPL/IR is that 'they' don't want you to have them.
Whereas the US enjoys a far less congested and crowded air traffic environment the Uk does not. If you are in an airway in your light aircraft with 6 on board you are taking up as much resource as the average airliner with 200 on board. In fact more due to your speed and lack of systems such as TCAS.
With the resource being finite and under such intense pressure the natural response of the regulator is to create barriers to entry.
Not fair but thats how I see it,
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