<< I think there are a lot of people that don't realize that these patents are VALID in the eye's of the courts, jurors, and memory manufacturers. >>
Whether they are valid in the eyes of courts or jurors is not yet decided. That's one of the points of the several lawsuits by Rambus and against Rambus pending in various courts around the world. Memory manufacturers are also undecided, although the majority is slowly siding with the ranks who agree that Rambus's patents are valid.
<< THAT is why, I believe, that Rambus has not been challenged to this point... not because of court costs & lawyer fees... >>
I certainly wouldn't say that Rambus has not been challenged. There are a wide variety of legal fronts that they are being challenged on, primarily by Micron.
Patent cases are a bit of a craps shoot. Neither Rambus nor any other manufacturer really wants to go to court over this. If Rambus's patents are legitimized by the court, then memory manufacturers will be in an even weaker position than they are currently in. If Rambus loses, then Rambus's stock will plummet and they will most likely cease to exist as a company in several years time (they have not made many friends in the industry and no one is likely to support any future technologies from Rambus if the legal threat disappears). This is the reason that it has taken so long for litigation to start - no one really wants to go to court. It really took Micron, who seem to have a personal dislike for Rambus, to really spearhead a counter-effort. In a way Micron is betting the future of their company on the outcome of this case... which is something that no other company had been willing to do.