The piece that the spark plug wire connects to, on the end of the spark plug, is threaded on with the Bosch platinum I've used. They aren't screwed on tight either (only finger tight). With time this can cause a poor connection. This happened on one of the plugs in the wife's 2nd gen, and the probable arcing from a loose fitting caused a failure of the boot with the spark arcing to the head (resulting in a really lousy running engine).
I suggest that you tighten down any screw on connector before installing the plug. NGK's aren't designed like this and don't have the potential problem. I wonder if some of the reported degraded performance reported with Bosch plugs are due to this.