Back in the good old days, if you were thought to be good enough to get a chance, once you were picked you were given a fair tilt at showing your wares.
Under this current policy, the likes of Steve Waugh and Matt Hayden, two blokes who took quite a while to find their feet and did so only through persistance on behalf of the selectors, they would never have kicked on. As we all know, they both went on to repay the selectors faith ten fold.
Someone like Usman, could very well go on to be a batsmen in a similar mould to S. Waugh if the selectors persist with him, but by the looks of things, we may never know. If he kicks on under this current policy, it will be an absolute miracle imo. Hows a bloke ever supposed to develop any confidence if he's given the flick after being run out in his debut? Even if he gets another shot in three or four games time, whats the poor bastard supposed to think? He'll be shitting bricks at the prospect of making a minor error and being sat out again for several weeks / months.
Far better off saying "Here's your shot Usman. We'll give you 4 or 5 games at this level to show us something, regardless."