One has to be aggressive in protecting one's trademarks, because--at least it's my understanding--failure to do so weakens them to the point of possible forfeit. That's why George Lucas had to go after the US gov't over "Star Wars" as applied to SDI, even though it was pretty much a lost cause from the get-go.
So if Marvel's legal beagles genuinely believe their trademark is possibly being infringed, they literally have no choice but to file suit. The outcome itself is almost secondary to taking the action. I do not believe for an instant the notion that they're doing so just to try and make money from settlements or wins. There are so many more effective and assured ways for Marvel to turn a buck than the wholly unpredictable option of litigation that it's just too silly a notion for me to accept.