Hi illiad, sorry for the late reply.
JB ships with Chrome as the default browser so playing Flash video in the browser a non starter. Also the Flash player won't download onto the Nexus 7 from the Play Store. I have heard tell that if you root your Nexus 7, side load Flash player and use a third party browser you can play Flash video in-browser. I've not tried this so can't comment.
The YouTube app works as it does in previous versions of Android and HTML video plays in Chrome. All the video links you posted either played in Chrome or launched the YouTube app.
I didn't cover this in the article as I didn't consider it part of the story of what's changed from ICS to JB though I should perhaps have mentioned that Chrome has now replaced the old webkit browser as the default.
Hope this clarifies matters.