There is something called ACF50....
I have never had a problem with corrosion on any bike from any maker that i have looked after from the beginning. Sure, i have inherited corrosion issues even on young bikes i have bought used and my hex GS and also my K1200 (brick type) had numerous other issues mostly around final drives & leaks of various kinds from oil to water to petrol. But no corrosion.
Its all about what kind of miles you do and how you look after stuff. In fact I am of the opinion (like others here) that other makers are no better in that department (Honda certainly has fallen off the proverbial quality cliff of late, whilst all others have always been on the "sh*te anyway" end of the spectrum).
BMW however do have the best aftersales at least in this country and the best no questions asked warranty. Thats indisputable.