Spin is important in T20s in general. Fast bowlers are simply easier to hit, but with spinners (esp. early on) the ball doesn't come on as well, draining the runs and forcing the batsman to play risks inside the powerplay. Ashwin was fantastic at doing so in the IPL, I feel we may have missed a trick by not selecting him for that one sole reason.
With our fast bowlers, barring Zaheer, in such woeful form, I am more than game to play 3 attacking spin options. Harbhajan-Ashwin-Ojha would've done the trick for me, instead we've got a few hapless seamers and freaking Piyush (who has the record for being hit for the most sixes in like all of the IPLs)