Yeah, that is fairly normal.
You can get shims that go under the plug sealing washer that allow you to 'index' the plug so that the ground electrode faces in the direction of the dark spot. This will sometimes allow a bike's engine to be more foul resistant.
Mark the plug's nut and install it, notice which direction the ground will be facing, spacer it to get the ground aligned. Sometimes it just takes a leeetle more torque to get a plug there(be careful doing this!)
Ever notice how once in a while you get a 'good' spark plug, seems to last forever and doesn't foul? Chances are that that plug just naturally indexed itself.