Good post.
I would add that it's important to test the way a web page works after every edit too. It's very easy to test thoroughly when the page first goes online, then decide not to test after edits because you think "It's such a small edit, it can't possibly affect the page operation", but sometimes it does! A few days after doing some edits you wonder why it isn't working - and all the people who have been frustrated.
Not that I do shopping carts, but the same applies to dropdown menus, edited hyperlinks, videos, javascript items, PHP forms, etc.
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.