Pakistan definitely have some talents and it's wrong to say that doesn't manifest in their Twenty20 sides at all. In T20 they have a good ability to get away with risk and come up with 150 runs (don't dare tell me that risks are not cricket), a brilliant synergy with their bowling attacks that very rarely concede more than that.
The trouble in longer forms of cricket isn't so much a lack of concentration as it is the missing bits in their game. If the boundaries do not come, then the runs do not come. They don't have a lot of batsmen who are masters of middle ground, just working the ones and twos all day long, so it is extremely easy for an accurate bowler to tie up a Pakistani batting order. It's simple logic that they eventually have a thrash.
In T20, they just keep looking for the ball in the hitting zone and often enough, it brings them runs. In Tests, they do show periods of patience, because they just do the same thing, just with different hitting zones. The biggest problem presents in ODIs where you can't afford to only score a boundary every 3-4 overs, nor can you afford to be out of batsmen after scoring 150. The missing singles are the key.