DrTak makes some good points. I spent a lot of time at a big city animal shelter as a student vet tech, and I also question the 90% purebred puppies figure. I also know that many of the adult dogs at the shelter had severe behavior issues and would sometimes show up again and again, as people were charmed by the dog and then got them home and discovered that they couldn't manage the problems.
The problem is not that prospective pet owners go and seek a companion they want to share their life with and obtain it from a responsible breeder or retailer, or even from a neighbor's backyard. With dogs and cats, the problem is overpopulation. With parrots, the problem, as DrTak points out, is false expectations, lack of knowledge, and lack of commitment. But even with the most loving and responsible of pet owners, stuff can happen: death, illness, and other disasters that life throws their way. There will always be sad situations. The best we can do is keep our hearts open ... to the pets and to the human beings who are doing the best they can at the moment.
(So sorry if this was preachy. Just my thoughts at the moment.)