The problem is what is called "Prior Art", if somebody has done it before a patent can be disproved and invalidated. For something to be patented it has to be novel and not obvious. Almost any idea in RPG's is not novel, and if somebody wanted to fight it they'd have a pile of prior art claims. Within the US at least, the Constitution lays out the actual legal foundation of copyright and patent law, and specifies it is to protect the creator/inventor of the discovery, not the first person to rush to the patent office on something they haven't actually invented yet and wait for somebody to invent it so they can profit. There's a huge gulf between what people file and never gets challenged, and what actually goes before a judge and argued.
The patent office has the general policy of granting any patent filed, even ones they know are dubious. They only reject patents outright on things they consider utterly impossible (perpetual motion for example). Their standing policy is whenever in doubt, grant it and let the courts sort it out.
For example, I wish I could recall the details, but a pharmaceutical company that saw that the patent on one of their medications was about to expire, filed for a new patent on one of the metabolites of that drug, that is: a chemical your body produces after taking the medication, and they patented it to prevent anybody else from making that medication because once consumed it the patient's body would produce a substance they patented. It didn't hold up in court when challenged, but they filed it.
In another case, Smuckers patented the peanut butter & jelly sandwich, so that no other company could rival their sold prepackaged PB&J sandwiches, and that patent was thrown out with a very strongly worded opinion from the judges when it went to court. The idea of pinching the crusts closed on a sandwich couldn't be patented, the courts held. (
http://www.msnbc.msn.com/id/7432980/). That news article also claims that only about 65% of patent claims are actually approved.
Could somebody file a claim to patent RPG's? Yes.
Could that patent get approved? Maybe.
Could that person get a lot of (bad) publicity and noise by threatening to sue everybody unless they paid him royalties on everything? Yes.
Would that patent hold up in court if it was challenged (If WotC tried it, White Wolf would lead the charge, doubtless, if anybody else tried it, WotC would lead the charge)? No, there are pretty blatant decades or prior art claims.
Patenting a genetically engineered creature is one thing, that's a patent on something that took work and effort. I'm a little wary of patenting genetically engineered creatures, but that's at least technology of some kind.
Patenting software algorithims is at least a novel mathematical concept, some bit of discovery or development. Again, I'm against software patents, but there was at least some R&D that went into the concept.
Patenting RPG concepts is trying to claim exclusive rights to something you not only didn't develop, but may have been around for longer than the patent lawyer you may be dealing with. Imagine the pile of books entered as evidence, Gary Gygax and Dave Arneson giving testimony that they first developed the medium, with possible claims leading back to wargames of antiquity or theatrical groups.
The CCG patent was on the idea of specifically denoting status of a card by orienting it, not on the concept of a card game played with randomly distributed trading cards, not on distributing cards randomly, and to be honest, the "tapping" mechanic was unique at the time; Magic was innovative at the time.
If, big if, somebody comes up with a radical new idea that completely changes the industry, some new method that completely changes the gaming industry, then that could be patented. Something as revolutionary as WizKids "clicky" bases or Magic's "tapping" mechanic.
Edit: Obligitory I Am Not A Lawyer, just a well read layman who keeps abreast of the issue.