In this day and age, I don't think "well-regulated militia" applies. Back in the 1700s, you couldn't deploy a Federal army in a matter of hours. If Spain decided to overrun Georgia(which happened while under British rule), there was no quick way to assist them as a country. Of course, this applied to any state. And, naturally, a band of criminals could ransack an entire town before outside help could arrive(or even know of it). So people had to have the ability to defend themselves.
So, while well-regulated militia is obsolete, I don't think the ability to defend oneself is. That's why the 2nd Amendment is still relevant.