Originally Posted by
London commuter
If you watch, the front hasn't stopped completely. It is just turning too slowly for the deceleration of the bike. With practice this is easy and it is a good skill to have - lets you know what your maximum safe braking is.
In any case, it hasn't "locked up" as in stoppped. That might happen on loose terrain but on good roads and grippy tyres I don't think it is possible.
I believe what the previous posters were saying is that your "maximum safe braking" should be less than the amount of braking you would get by just clamping down on the brake levers and performing a spectacular faceplant. It is VERY possible on good roads with grippy tires to completely lock up the front wheel and end up losing some teeth. The back wheel skids because the bike's center of gravity can't pivot around the back axle... but on the front wheel, if it's completely locked, the wheel can still pivot around its axle, sending you over your handlebars.
The point is, you already have the ability to brake too much if you for some reason wanted to... so you already have more brake than you need. No reason to risk warped rotors and a host of other problems just so you can have more overkill.