I would suggest that:

1) It isn't the same situation. The level of corruption and absolute poverty levels are not comparable.

2) Where there are similarities in "first world" countries (e.g. empty housing stock), eyes are very definitely batted. At least in the UK.

3) I would argue that 10 million empty homes in India, where there is significant slum situation, which is basically accepted and regarded as "normal", even in the capital city, is more eyebrow-raising than an empty home situation a "first world" country. I don't actually see anyone losing their minds though.

I'm sure a significant contribution to this are NRI's purchasing from abroad where their earnings abroad give them greater power back home than in the local market. Whilst some people may rent out these properties thus serving that part of the market, others want to hang onto a new build / never lived in property. Some might say this is a form of insurance should they wish to move back, but its most likely just an investment that doesn't serve society.

And yes, this is very similar to investments made in London/New York/San Fran, but wealthy individuals trying to offshore their wealth, although these properties are typically rented out.

A quick google says 18.6 million for the US, so I think you're right on to question this.