Apple defied critics again and turned in strong quarterly results, while its value soared on an increased investment from the ever-influential Warren Buffett. But the smartphone maker remains hugely over-reliant on one product line, the iPhone, and needs to convince its partners and shareholders that it has convincing long term plans to diversify its revenues, while protecting the crown jewel against challenges from Samsung and, in particular, the rising power of Chinese phonemakers. Currently, Huawei is the most threatening, now it is in third place in the smartphone market worldwide and has some high impact models. But its virtual exclusion from the US market for mobile infrastructure seems to be spreading to handsets (AT&T and Verizon both recently dropped plans…