That's the problem with Airtel, it is user friendly only for HD users and not for SD. Even I was planning to buy new DTH for my second TV, now option is Tata Sky. I will wait for 1 month, if airtel adds MTV HD, MTV BEATS HD AND VH1 HD, I will upgrade to HD.
It's user friendly for both. Also u can simply buy HD box and activate SD packs if u still have some doubts or problems going on SD connection. Missing Viacom18 HD music channels have nothing special in them hence ur decision should not rest on their addition, this is my honest advice