The tab you posted there is a G major scale.. My best advice is to forget your classical knowledge for a while and just learn the guitar with western music theory. Once you have learnt the theories of music ( I meant western ) you can think about combining your ideas of indian classical to it.
and to answer your question of why so many ways of playing the same note on the guitar.. well, if you get advanced enough in guitar you will start to play sweeps , tremolo pickings, slides , alternate picking, legato , etc,.. etc.. which will be IMPOSSIBLE if the guitar isn't designed this way.. and of course this allows players to play a variety of chords such as Em M7 ..
So my final advice is empty your mind and learn guitar the way it should be learned..
Cheers. Happy guitaring..