Both a word and a game clone are very often protected by I.P. laws. Words can be a trademark or a copyright. Games, no matter how derivative, can be protected from piracy. Their titles often cannot be used by another person. Characters and what not (eg Mario) cannot be used without permission.
Note that I am neither defending nor condemning the practice. Just pointing out how the American system works. IP law is very powerful.
I see a small flaw in that logic, however. If anything created (ie, Mario) by one person/group can never be used by another person, then there are millions of law breakers all over the world, who create Mario fan-art, Mario-esque games, Mario crochet dolls, etc.
It has not been stated that something protected under IP laws cannot ever be used by another party. There are licensing agreements and a variety of other ways in which a property owner can allow others to use something. Note the owner still has control.
Things you mentioned would mostly fall under the doctrine of 'fair use'. This is a broad exception under most IP schemes in which a party may use a piece of IP without consent of the owner. However any diminishing of the value of an IP or profiting from an IP is almost universally protected. Some companies are far more aggressive in policing this than others.
See Games Workshop as an example of an aggressive company. You cannot even post a fan-made adventure online without drawing their ire. They made Boardgame Geek take down hundreds of fan made cheat sheets and player's aids. Nintendo used to be very aggressive with who and who cannot make games for their systems. They still might be. I don't know. Lately with the rise of emulation sites it seems Nintendo has backed off of certain things. Another good example is the South Park guys. They post all of their shit online about a month after airing. They'd post it immediately except for their studio objected.
I could go on and on. Attorneys tend to blather.
