I own over 300 DVDs and I am a Netflix customers. Basically I buy any good title that comes out ( I hit bestBuy every Friday) and my wifes rents anything she wants that I didn't buy and that she wants to watch.
It works out so well, there's only 4-5 titles in my collection that I wished I had never bought ( Tomb Raider 2 : Craddle of Life being one of them, that is like one of the worse movie ever!).
Anyway both renting and buying have their space, but you tend to buy those movies you like more or that are generally considered as better so I would guess most people are more likely to try to get those in higher quality( Blue Ray)