The answer lies in our approach of un-complicating finance.
When we (any investor) invest in equity, we are aiming for returns at par or better than the asset class. The Nifty provides us with a widely known and available benchmark that represents that asset class return. The Total Returns Index is usually tracked only by institutional investors. Our audience who are primarily individual investors, relate to the Nifty much better. It is easy for everyone to look it up in the daily paper and verify.
We are always looking for the practical and convenient versus the precise but complex. We are confident that the Nifty provides a good approximation even of the Total Returns Index. The dividend yield in the Indian market is historically 1.3-1.5% (relative to the long term equity returns of approx. 16%) and the Total Returns Index reflects that. However, what the Index does not consider is that if one were to take a position in the Nifty, there are some transaction costs (e.g. brokerage, account fees, etc.) associated with it. We believe that these costs, to some extent, offset the dividend yield component making the Nifty a good enough benchmark to work with.
The idea behind benchmarking the track record is to showcase the benefits of investing in the equity markets through a scientifically selected basket of mutual funds which historically provide a return significantly superior to the benchmark after considering all expenses. The use of the Nifty as a benchmark does not dilute that conclusion in any way.