One major problem that Prasad inculcated into our bowlers is, vary your speed as per the wicket's condition. So on slow wickets, guys like Ishant, Nehra and Munaf will also bowl at slower speeds. On tracks that give good pace and bounce, they will touch 140+. I have never seen Lee or Siddle or Johnson reduce their speed on a consistent basis on slow wickets. They vary their pace a little more on slower wickets but they still bowl at their optimum for most of the time (atleast 3-4 balls out of 6). The Indian bowlers barely touch their optimum speeds in the process.
Ishant has to consistently bowl 145+ and vary his pace more on slower wickets. Zak should be bowling 135-140 consistently. Munaf should be bowling 140+ consistently. Same with Nehra too.