I identified that I can comment out this line
Code:
<a href="$INTRO_URL_VALUE">$INTRO_URL_TEXT</a>
in email/email_template_checkout.html, but I think that will only take care of html emails, right? Not text emails?

The thing is, that's not the only problem: the order confirmation screen has all the stuff in it about a temp acct being set up, and a logoff button, which does NOT show when using credit card payment and COWOA.

So I was looking for a more 'elegant' solution than just commenting everything out. And I'd also like to actually understand what's going on.

I do think that for some reason, that COWOA switch is not being thrown when you pay with PayPal Express Checkout. It all works beautifully when payment is through PayPal Website Payments Pro.