Although Download Helper and numerous other extensions will work, there are two problems, 1) its generally either illegal or at least against the sites T's and C's and 2) Only a small proportion of people actually know about them and care enough to work out how to find, install and use them.
Look at ringtones - how easy is it to strip a small section of music from the full track, and yet companies have made millions from people willing to pay pounds at a time for the 30-second clip to be made for them and delivered straight to their phone.

Haven't these n00bs heard of DownloadHelper?
I've been downloading every Flash video I liked since God knows when.

"Revenue-generating tool" LMAO @ the monniboyz ...

@ A/C, HH, and all others.

Drawbacks as in back to the drawing board, why? Simply because the video junky that would buy would want to recoup some of the cost by opening his own site with the bought content posting it for free and reap small ads revenue.

I don't see the value in doing this for money cuz, video clips gets stale real quick. Unless unless your contented with meagre ads revenue.

..But average 6 pack joe wouldnt know how to use a screen recorder nor probably heard of firefox :D:D:D....

there are plenty of browser extensions that will grab an embedded video stream, and if youtube block that then there's always the trusty screen recorder.