Have you seen a shelter in the US? It's really easy to point out hypocrisy, but where exactly does that website do anything more than bemoan the problem, rather than offer any sort of solution? Shelters are over crowded, under funded, under staffed, and drive some animals mad.
Further, PETA isn't PAAAD. "People Against All Animal Death", I think that "ethical treatment" does not exclude death. Maybe in a perfect world, but in this day and age you have to take what you can get. For me, the biggest issue isn't animals being put down, which is sad but should take a backseat to animal mistreatment, cruelty, and suffering. As such, if an animal is in such a state that it's future is just one of pain, maybe euthanasia really is the ethical course.
We can't know the circumstances under which those animals came into PETA's hands exactly, but the vast majority of them were "Surrendered by Owner" at least. I have a hard time seeing "Surrendered by Owner" animals being those with a bright future; some of them were probably simply put up for adoption then fell into PETA's lap eventually, but I'd bet just as many of them, at least, were those that owner's mistreated and gave up on. Do you think those animals really have much of a future, competing against other non "damaged goods" animals for the increasingly scarce chance at being welcomed into someone's home?