http://www.theguardian.com/world/2015/jan/31/india-economic-...
Imagine if you had cargo truck borders and customs paperwork between every one of the US 50 states and what a nightmare it would be for trucking/logistics/distribution/warehousing/cold chain/etc.
Indian states have a significant degree of regulatory autonomy, far beyond what a US state or a Canadian province has, to the extend that some states are looking at banning alcohol entirely and others have unique tax code and criminal code laws not found in the rest of India.