In Bangalore they provide total 27 HD channels. 2 are HBO HD channels and 1 is Star World Premiere HD. For these 3 channels you need to subscribe separately. So your annual HD subscription is for watching 24 channels. They are planning to increased the HD count. Once they are done with their work at back end, they will have lot of bandwidth to add more HD and SD channels.
As of now, you can have only HD channels without subscribing to any SD channels. But, once the packages(similar to DTH packages) are pushed to customers, I am not sure if it is possible then.