Going on memory (again) so bound to be wrong
I seem to remember something in one of my PPL books that if the static port gets blocked then you can get around the problem by smashing the glass on one of the instutments to provide static pressure to the systems. Somewhere in the text it was mentioned that the static pressure being provided from within the cabin would usually be slightly higher than from the static port but that the difference is usually so small that it is negligible. By adding one and one together and getting three, could this be implying that CBLong's assumption are in fact correct but the difference isn't large enough to allow a typical C152 pilot to notice
D