Hi Manish Agarwal,
Much to our regret our blend support for some of the controls is less than perfect. It is our top priority to immensely improve in that area for our 2010.Q1 release. Until then such styling cases can only be resolved by manually writing your style in XAML.
I do understand the inconvenience this shortcoming presents to you for which I apologize.
All the best,
the Telerik team