[pjsjr13]

Who is going to bother developing tuning gear for the 3-cyl Cooper? The majority of buyers presumably aren't after a performance gain, as they would have bought a Cooper S - and buying an S is likely to be much cheaper than tuning up a Cooper.

Not always the case. There are a few owners that are autocrossing the Mini non S. There are some handling advantages with the 3-cyl. Personally I think the aftermarket will warm up to the 3-cyl.