From what I gather so far from the two episodes we've seen of 'Eureka', the town was created as a haven for the country's greatest scientific geniuses where they could work on their top-secret projects in secrecy, security, and seclusion. (As I crowed last week, "Triple Sec!")
But so far, Marshal Jack Carter and his daughter have wandered into town after a car accident and the original Susan Perkins showed up there deliberately in order to find answers to her questions about the other Susan Perkins who was murdered at the end of the pilot.
All I can figure is that the government didn't want to draw attention to the town by making it invisible to the naked eye. And this is something we know they can do there because that's what happened with Global Technology.
Outside the parameters, the high-tech research facility and its grounds are invisible. Looking in, all you can see are woodlands beyond an old creaky bridge. But once you pass through the barrier, the gleaming edifice is there in all its architectural glory.
Maybe that's all they really wanted to protect from prying eyes. And with the town surrounding it in much the same way as a moat around a castle, perhaps the authorities figured that this solution would be easier than to seal off than the entire town.
After all, some land rapis- er, developer might see the woodlands and seek to get the rights to raze the territory and build condos. And the scrutiny and ensuing questions as to what's really there and who owns it might draw the attention they're trying to avoid.
Still, shouldn't there be elite Special Forces posted at all roads leading into Eureka, working undercover as park rangers, in order to keep people from wandering into the town itself?
Just askin' is all.