If i was a first time buyer - I would certainly be looking at the sales chart before parting with my hard earned money as it would lessen the risk of going wrong in the buying decision.
But in practical day to day life as someone rightly pointed out, if two cars are almost equal on merit, sales figure won't matter to someone like me. I would put down my money on something my heart says Yes and not to what the common Tom Dick n Harry are buying. Plus everyone should buy a car which suits there requirements better and should not blindly follow where the crowd is going.
For instance - one of my female cousin bought a Hyundai i20 magna diesel last july, when her only requirement was a hardly 10kms run daily. Her car has run just 3.5k kms in close to 9months now. A petrol would have been any day a wiser decision, but just going with the herd mentality, went for a diesel. Don't really know if she ever would recover her initial extra investment for a diesel.
For us, my Dad bought Fiesta Classic in 2011 just because he was in love with his previous Fiesta 2006 model which had started showing off its age by then.Sales chart, Duh!! Who gives a damn! He didn't even look as to what the competitors were offering.
Same year we bought the just launched Hyundai fluidic verna petrol over the Numero Uno in petrol segment "Honda City" just because the latter was way too common on the road.(Every person has his/her own way of thinking
When i got my Polo in 2012, there were like a hundred people who must have asked me why not a Swift or i20 for the same price. I was like sure that's what differentiates me from you. Pun intended! On a little funnier side, its more like if I love Golden Retrievers, why would i go buy a Dalmatian just because most of my neighbours have one.
For me its straight forward, If you love something,go for it. You won't go wrong in the long run by God's grace. Happiness is all that matters.
But not every car owner is a car enthusiast too.Majority are not.I would say more than 90% are not. So for someone who thinks about cars as just a daily commute or maybe a dying investment(as most of my relatives do), its better to look at the sales chart and get what others like them are buying and get more bucks in return than the pleasure of owning one's fantasy machines. P.S. - No offence meant to any other car owners,just my views.