Pot calling the kettle black?

Hi, First post and all.

This is kinda in reference to a post by Kate VN, titled 'but. but..'
I'm more interested in intellectual property (IP), and sampling when it comes to sounds, and sampling.

Joel Vietch has an amusing site called rathergood.com, in which he has all sorts of amusing songs and animations some which verge on being music videos, being made to accentuate or poke fun at established songs. Such as his viking kitten attempt of Gaybar by band Electric Six.

Joels funny animation (lots of Kittens)
http://www.rathergood.com/gaybar/

Rob Manuels faux doco of his mate getting ripped off.
http://www.robmanuel.com/2006/12/13/is-coke-ripping-off-the-little-guy/

The crux point comes as an example of a Argentinian coke ad surfaces where Coca-Cola seems to have ripped off another of Joels creations. Joels rights to his IP seem to have been circumvented. One of my friends ventured the idea that the fact that as Joel has clearly sign-posted the song in his video was written and played by the band Electric six that his animation is more legitimate, however.....does that mean if Coca-Cola Argentina had put a hastily scribed JoelVeitch@rathergood.com at the end of their ad that their use of his IP would be all right?

The main question I have, with regards to sampling of both audio and musical clips, is what are the general rules that are used to define and draw the lines between public domain and of copyright infringement?

Or more importantly, as both sites love to pull pranks on the general public have I just been the victim of another one of their hilarious scams?

Cheers
Mike-L