Actually Sri lanka and other asian teams hardly survive in the fast pitches of Australia or Africa or even England. Pakistan is doing really well though I have to say, considering they don't have any teams touring them. Yet maintaining a ranking
It is not entirely true as India has played matches and won in England and Australia and they have the best record outside the continent when you compare the teams in Asia and Pakistan is playing in neutral pitches in the UAE and was winning matches and so is the reason they are ranked higher .Every team is strong when they are playing in their home ground so there is nothing surprising about it.