I prefer the Gruenfeld lol.
Yeah, I think 1...Nf6 is the way to go lol.
However, 1...d5 is Classical.
Classical Chess will never ever ever be considered bad.
It is Classical Chess for a reason.
The reason is chess players through out history have tryed and tested these lines.
They are Chess Grand Master Approved!
It is chess at its finest form.
Direct Occupation of the center with a pawn.
Direct claiming of center space.
I believe the only reason 1...Nf6 may be considered more popular is due to modern chess GM players.
Obviously chess fans will try and play line's there favorite chess legend or hero plays.
I have found many chess players who support or are a fan of Vishy Anand tend to love playing Queen Indian Defences.
I am not a huge supporter of Vishy but I guess he has played some QID in his time and his fans tryed to follow in his footsteps so to speak.
Other players are like that as well.
You have Garry Kasparov or Bobby Fischer who like the Kings Indian Defence.
Which they have influenced my chess play little bit.
Since I have played KID and Gruenfeld positions similar to them.
The Indian Games are mostly Hyper Modern Games.
Which it is really hard to see how Indian Games and Classical Games will ever be considered bad.
I know I rambled on a little bit;however, I wanted to kind of answer your topic question and why Indian Games may be considered more popular.
I do not believe they are better by any means.
I simply beleive it offers different positions for different players.
I'm just killing some time waiting on something here before I play a few games tonight. I'm searching through games in ChessTempo's database and exploring different opening systems, etc. Let me ask you guys something: Is the QGD and Semi still viable at the Expert and beyond levels of play? It seems that the numbers overwhelming support Nf6 Indian games in response to White's d4 but I can't be the only one who doesn't necessarily want his response to involve surrendering the center to white immediately.
On the flip side - I open 1. Nf6 with white and naturally am always in Queen Pawn games. If I started following a d4 response as black that went into the Indian games, I'd obviously be encountering the same lines in many cases.