You are right in general, but note that for instance there are still many 2 stroke auto rickshaws: http://www.autocarpro.in/news-national/karnataka-ban-polluti....

Typically, the game goes as follows: new laws get drafted, local groups such as auto rickshaw unions get together and demand time/cash incentives to move to more expensive, cleaner equipment, local governments grant extensions, and the cycle repeats.

Then there are the general issues plaguing enforcement in India, which are listed in the wikipedia article.