The most recent document I could find from an official source is this one, dated July 16, 2015 and posted to the CBP web site on August 11, 2015. An excerpt:
Citizens of the countries listed below are exempt from the six-month rule and need only have a passport valid for their intended period of stay.
One reason this information is hard to find is that it is intended for "carriers," such as airline companies.
Another great way to check these requirements is TIMATIC. Certain airlines have a web page allowing you to query TIMATIC; the pages are generally labeled along the lines of "check visa requirements for your trip."
For example, on KLM's website, you can follow "prepare for your trip," and then "passport and visa," and then, under "which travel documents do I need," there's a button for "check your trip." It links to their TIMATIC query form.
Specifying India for both nationality and embarkation, and United States for destination country, I got, in part, the following:
- Passports issued to nationals of India must be valid for the
period of intended stay.
So it seems that anyone who's telling you that it must be valid for six months beyond your period of intended stay is incorrect.