It's all a matter of intellectual property.
Sega can't own a patent on the Sonic the Hedgehog character because it's not a process as such. But it can, and does, have copyrights to the Sonic brand, and to the codes used in the games.
In the UK at least, copyright stands for 100 years. Hence, new books can only be published by the copyright holder, whereas classics can be published by anyone who wants to. I can't see why legislature would make this less favourable to copyright holders, especially to just 5 years - why would a government be motivated to do that? You won't find many politicians on X-Box-Scene or hackers sites, etc.
Even if you drew and coded your own version of Sonic, if it was too similar, and deemed to be intentionally intended to perceived as or mistaken for the Sonic character, than this would be deemed to be copyright theft.
I'm no expert but I'm sure we're all aware that intellectual property is fast becoming an even more tightly-grasped concept these days.
But it's fair to say also that many things in the media are 'illegal' in that they, intentionally or otherwise, infringe some kind of copyright or patent in some way. After all, SEGA has a patent for a taxi game. And some big research company is suing eBay at the moment for using a transaction system where a third party is used to negotiate a sale (fixed-price auction format). These seem like pretty strange things to 'own'.
However, I read that most litigation re: patent theft is actually lost by the claimant or dropped before the case comes to court. If a defendant can prove that a patent has been widely-used for some time without being claimed by the patent holder, than the patent can become invalid. For instance, if someone had patented the television three-hundred years ago, and the family's estate decided to sue television makers only now, then they would have no real case.
I guess it only really becomes an issue if you intend to make any money out of your potentially copyright/patent-infringing product, or if it becomes notorious enough to be deemed to be damaging to the original brand.
Then again, a small cafe in the quaint English village where I used to live was threatened with legal action by McDonald's because it was called McDermot's - in the end they changed their name after doing modest business for 20 years. Go figure!
