And they're also forgetting that no link, even one from a page with a lower PR than yours, will decrease your PageRank. Those PR3 links do help, even if to a smaller extent. And of course, if it's a link exchange in question, the link back to the PR3 helps to bump it up and so make it eventually a more "valuable" link.
I certainly understand and support having some standards as to what link exchanges one will accept. But PageRank can't be the only measure of what is and isn't a good link.