Unfortunately this is just a symptom of vastly superior consumer laws in the US. Exactly the same happened with my Audi 1.8T - sump pickup pipe was liable to blocking due to coked oil returning from the turbo. Audi of America issued a recall on all the engines to fit a bigger pipe. Audi UK said a recall was not required, despite identical parts.
6 months later my sump blocked while I was on the motorway, complete loss of oil pressure, warning lights everywhere, had to pull over on the hard shoulder and call the AA. Audi repaired it and sent me a bill for £800. I complained and sent them copies of the recall notice from the US and they were not remotely interested. I then threatened to take the story to the press and they offered to pay 50% and that was it.
Basically in the US they have the concept of a 'class action' lawsuit, which means a single lawyer can go to court and sue BMW on behalf of every N20 owner in the country for supplying a defective/unsafe product - which obviously would cost BMW enormously. So in the US it's cheaper for them to issue a recall. In the UK no such legal option exists, it would require each N20 owner to take BMW to court individually, which most people don't have the time or resources to do. So BMW play the odds and assume less people will sue them in the UK than it would cost to issue a recall. Result: issue exists, but no recall for us.