Some very cheap 165mm cranks are alternatively-drilled 170mm cranks, but not many. My old Thorn Nomad came with (cast, not forged) Dotek cranks of this type, which were ugly, heavy and probably not very strong. I replaced them with Sugino cranks eventually.
You still get the extra clearance in most cases, because the outside of the pedal is usually the first thing to hit the road when the bike is leant over. However, there is so much traffic-calming clutter on the roads now that you could conceivably catch the crank itself on the kerb of a chicane, or on a raised mini-roundabout (I've done the latter). Off-road, it's common to clip rocks with the crank. My MTB ones are often scarred. As with fixed, sometimes you have to keep pedalling through obstacles on an MTB, usually for fear of stalling on a climb.
