I would like to add that pretty much everything has been invented already.
How much innovative content can you find in any modern game (any genre, any platform)?
When you analyze some thing that you think innovative, chances are that _that_ same thing has been first seen in another game, likely much older.
In part I believe this is fault of Publishers, who are 'forced' to bet on sure wins, because the market is merciless - and when millions of \\$\\$\\$ are involved there's no room for failures.
This in turn falls on Developers, who have closer and closer deadlines to slavelop the new dreamy game the people want.
The other part of the fault is that, well, seriously what's left to invent anyway?
Think of something cool, and then take some time to find out if that something has been done already.
Any genre, any platform... eventually you discover that the idea is not new.
Probably the technology used was much different, quite surely the graphic is different... but the concept is the same, and your idea is not as new as you initially thought : (
This all is to say that even modern commercial games end up recycling old ideas and game mechanics, and thus you shouldn't worry about copying something and break copyrights.
So long you don't plainly rip-off contents or claim that yours are innovative, while they aren't, you are gonna be fine.
Quick Note: I think the gaming industry started to run out of ideas when the first Carmageddon appeared. The situation definitely degenerated with Carmageddon 2...
(my very personal opinion)
Ciao ciao : )