3) And why wouldn't road bikes need a disc brake? Won't it help to stop quicker?
Try taking a look at images of top pros that ride on major races.. None of them will have disc brakes on a road bike. And these are guys that pedal at 50kmph+ on an average!
Where disc brakes ARE required would be when you ride a mountain bike on REAL trails and mountains (not on our Indian roads, however bad they might be )
Also these mountain bikes are NOT the same as what Hero/Atlas might be selling..