Ganguly gives the reason for dropping Kaif
"Both Yuvraj and Kaif are playing well but Yuvraj has a better Test record than Kaif at the moment." - Ganguly, at the end of the first day's play.
Yuvraj has scored 302 runs off 10 innings with an average of 37.75, while Kaif has 294 runs to his credit off 13 innings with an average of 24.50. Seems like Kaif would have to wait for Yuvraj to fail in a few innings and get his average lower than 24.50. And then Yuvi would wait till Kaif's average falls down again. As some one (Harsha) said, if you play for averages, you will end up playing average.