Indian etiquette is quite formal, a mix of both Western and Asian culture.
Many Indian families do not keep alcohol in the home.
It is not good manners to say 'thank you' at the end of the meal. Invitations should be sent out early, and follow up phone calls should be made close to the day of the event.
This is considered as an inappropriate and impersonal gesture. In Western etiquette this would be considered extremely bad mannered, but be prepared for the fact that your guests will more than likely be late, since arriving punctually for a social invitation is considered bad manners in India.
It is tradition and part of the Indian culture, it is also an accepted part of Indian etiquette.
Although very few people practice this part of Indian etiquette when dining in the 5 star Westernized hotels and restaurants - but try to remember, it is good etiquette to fit in with the culture wherever you may find yourself.