I've always felt depression is only somewhat understood, as you say it's hard to diagnose.
For example, #7 is a common one for me - and you simply can't see it or diagnose it unless I tell you. But you can usually tell from other things; like the fact I get obsessed with ideas and spend a lot of time walking (i.e. thinking/brooding).
I agree with you; and I wasn't exactly trying to make a diagnosis over the internet. I was trying to point out that although Taren seems so certain he was not depressed, she makes some claims which are very much not the be-all-and-end-all of depression. And that some of the activities she describes are common tells for depression.
My point being; it's not simple, and depression is a complex and evil thing.