Many pieces of equipment with cross-headed screws actually have Pozidriv screws rather than Phillips screws in them. This is especially true of Japanese equipment. [EDIT 2007-11-26] Or are these yet different JIS screws? See the updated post about this here.
I bought a set of Hozan [JIS] drivers, but now that I’ve learned that PB makes them [maybe] (see tools article) I’ll buy any additional ones from them. Pozidrive screws have “tick” marks between the slots–or should.
Here is an interesting explanation of the different screw heads in the context of cabinet/furniture making.
After some testing with both Phillips and Pozidrive drivers, it seems that some/many of the inexpensive screws that come packaged with home hardware-type items are non-descript and perhaps don’t meet either standard!