They should not just be testable, but should have tests. Under ATDD (which I accept is not necessarily what she's describing here), a requirement without a test is not a requirement.

If you've got a project with a lot of complex business rules, this makes a massive difference to whether they're correctly interpreted and implemented. You can argue with an English sentence, but it's a lot harder to argue with a worked example (or a bunch of them).

Well, yeah, that's one of her few points in this tiny article.