You're only going to high-sided if you've allowed the rear wheel to step out from behind the bike though. in most situations, the rear brake provides the opposite affect, and actually keep the bike tracking straight(er). I think the 'logic' behind laying the bike down is giving yourself a choice of HOW you want to impact, once that impact is perceived as unavoidable. As someone mentioned, if you know you're not going to stop in time, you have a choice of hitting the obstacle head-on, or dumping the bike and probably hitting the object with your legs first. it's the 'baseball slide' instinct. personally, i think you're almost always better staying with the bike, unless it's a semi or something yuo can legitimately slide under without being harmed.