I think Phillips is used because it's easy (easier?) to get Philips in smallest sizes, like 0, 1 and 2, while I have yet to see normally priced set where Torx is present in smallest sizes (based on my experience, what you can get is about from T6 and up; but you will be hard pushed to find hex(allen) keys under 2mm as well)
Also, based on it's classic Phillips (not Pozidriv), I think the reason why it's not used for other screws is that Philips is designed to cam-out once you reached certain torque - that doesn't help long life of the screw (and driver) at all. Not that much a problem with very small pocket clip screws but certainly not good with e.g. pivot pin or frame screws.
I've already propsed in thread @ Spyderco forum that Spyderco should make it's screw sets used on it's knives unified (as e.g. Benchmade does).
I'm not big fan on hex (allen) screws either as they are in two standards - ISO/DIN (metric) and ANSI/ASME (imperial). I think it's the very reason why you won't find hex but torx heads on European made Volpe.
I really hate this situation when there are different "standards" - they are not the standards anymore, are they?
(FYI There is a difference in screws' threading as well! Try to buy screw with different threading :thumbdn
