Personally, I don't think that disassembly should void a warranty, provided the knife isn't riveted or pinned together. However, improper disassembly/reassembly should certainly void the warranty, just as improper use/abuse would. But I can certainly understand why a company would prohibit disassembly, as protection from idiots who don't have the proper tools or mechanical ability. I have willingly and knowingly taken apart several of my knives despite "voiding" the warranty, like Spydercos, Benchmades, and Microtechs. I put "voiding" in quotes because I would challenge anybody, even the people employed by those companies, to prove that I had voided the warranties.
I guess that you can't blame a company from protecting themselves from idiots. Such policies are undoubtedly the result of people who screwed up their knives by improper disassembly and expected the manufacturer to correct their errors. Even companies like CRK that allow this sort of thing have to deal with the occasional idiot that abuses their warranty and abuses their knife.
Good points.
In the end, they're probably protecting themselves from lawsuits and other such stuff.