That said, I found Onyomo still useful despite these limitations. MapMyIndia.com for example, has much more data and far greater level of zooming, detail and tons of features. However, it's also extremely slow because the page refreshes everytime one has to zoom or pan. Onyomo also has the advantage of using mapping data of an excellent source.
There's a dearth of good mapping applications for India basically because there's lack of good mapping data. Google Maps doesn't have street level maps of India (only satellite imagery of a few big cities). It's also difficult to find reliable GPS data. Recent initiatives by the Indian Goverment are set to change all that. In May last year Indian Space Research Organisation (ISRO) launched Cartosat-1, India's first mapping satellite. The 1560kg satellite will provide unique 3-dimensional "stereo satellite images" (compared to static images used in Google Maps) for the first time ever in the civilian world.
Gaurav on Onyomo.com
Eicher city map - Delhi
Stories on the launch of Cartosat-1 - SpaceflightNow, Hindustan Times
Indian minister on Cartostat mapping capabilities
New Scientist story on Indian space programme