Who are specialised openers and do we really need them??

Time and again whenever India goes to play a series outside the same question keeps on coming back. Who will open for India and by the middle of the series there are talks all over for new sets of openers. I was just reading an article by Indian Coach Greg Chappell and was wondering do we really need specialised openers.

I think atleast 50-75% of the times one of the opener fails in less than 10 overs when the ball is fairly new. Once one of openers fail a One down specialist batsman like Rahul Dravid comes down to bat. What it means if not all more than 50% of the times he is opening for India. Similarly if both the openers fail which has happen more often in this test series, the 2 down batsman also act as a opener. So now if your specialised openers are not efficient (which is the case in this series) then you are actually looking for your top 4 who can perform as openers..

Let's take this a little further what happens if your middle order batsman are good and they last the first whole day or may be India loses another middle order batsman (No 3 or No4) or may be both. So you are four batsman down at the end of the day. Next day the opposition team decided to take a new ball so now it's effectively same as opening the innings. So even your no 5 and no 6 needs to be able to work as make shift openers. That virtaully means your entire batting order needs to be specialised openers.

I know this is all hypothetical and doesn't happen very often but was just curious what really Specialised openers mean.

P.S. Sehwag, Tendulkar and Ganguly all were middle order batsman before they were made Openers. So do we really need specialised openers and if we do than I need to understand better WHO IS A SPECIALISED OPENER.