It's common for North American companies not to rate their vehicles for towing. I think it's fear of litigation. The only companies that provide tow ratings for their smaller vehicles are VW, Toyota and Hyundai. Everyone else shies away.
Example: I asked Subaru about towing capacity of the new Impreza (because I know it can tow 1000kg with a much smaller engine in the UK) and they replied that they'd invalidate my warranty if I mount a hitch.
BTW: I love the BMW Touring. Fantastic vehicles. And the Audi Avants.