Why batsmen are preferred over bowlers as captains?
A look at the captains of the present Test world indicates :
R Ponting - Aus - Batsman
M Dhoni - Ind - WK
Y Khan - Pak - Batsman
C Gayle - WI - Batsman
D Vettori - NZ - Batsman although camouflaged as left arm spin
G Smith - SA - Batsman
M Jayawardena - SL - Batsman
A Strauss - Eng - Batsman
Even if we take the names of past captains, we cannot see many bowling captains. Exceptions are there like the rotating chairs of Pakistan, Walsh for WI, Kumble for India, Flintoff for Eng etc. But 80-90% of all test captains in history have been batsmen.
Considering the fact it is undisputed that bowlers are the ones who win matches and batsmen set them up, it is slightly bizzare to notice the huge skew in favor of batsmen. And not that the bowler captains have done a terrible job. Imran Khan, Kapil Dev, Walsh, Kumble etc were excellent and inspirational captains.
But still it seems to be a tradition that teams prefer batsmen as captain. Australia for instance has not had a single bowler captain since the days of old Richie Benaud.