Legal argument:
It is called protecting your assets. If you don't others may be apt to infringe. And after a bit of time of not protecting your assets (names, intellectual property, etc) a court may not do so either. Vigorously protecting a company's turf, is not a prickish thing to do, it is just good business practice. Specialized has had the name "stumpjumper" for quite sometime. While I suspect that Specialized knew that the boys at Mountain Cycle had no intention of infringing of the name/trademark, they still need to protect against anything that could be perceived a sleeping on their rights (called the equitable doctrine of "laches" in legal jargon) so that others that may actually want to use the "stump____" whatever bicycle to directly compete with Specialized's Stumpjumper.
While the portion that knows about this may be bugged, the general public most assuredly could care less, and probably many specialized's potential customers don't even know that there is a Mountain Cycle bike company at all. In the end, it is just good business.
For an example see the Jeep/Hummer conflict. There Hummer had for years used a grill that was arguably similar in design to Jeep's. Both had seven slots in the grill. Jeep (Daimler/Chrysler) could have cared less for a long time while American General was indendent of General Motors. BUT once GM purchased Hummer, it was an entirely different ballgame, as GM owned Hummer was to probably directly compete with jeep products. Jeep then claims trademark infringement, claiming that the two companies grills will confuse the market. GM in one of its defenses claims that jeep effectively slept on their rights too long to now claim infringement. The court agreed. It is just smart to vigorously protect all of your property.
Lawyer hat off:
Still as a lay person, it smacks of picking on the little guy, who had no intention of ripping off Specialized trademark. Obviously, I don't need to state the facts here, but Portland and Mountain Cycle have some ties to Stumptown/Portland. There is a stumptown cyclocross race as well. It just made sense for Mountain Cycle to name their cross bike the"Stumptown." I am not sure what discussions went on before the lawsuit was initiated, but perhaps they could have been done better to avoid the negative publicity if you are Specialized.
