First up, here is what little I "think" I know.
Usermode exploits are game specific exploits that gives us access to anything that game would have access, so if it used a camera, we could have camera access, ect. Nothing more nothing less. That is what makes compatibility a problem.
Kxploits are exploits in the psp emu's kernel. These give us access to the whole, emulated, hardware. This means they are more compatible, but harder to find.
Now question time.
Kxploits are kernel mode, thus am I correct in assuming that they have nothing to do with any one game? You simply need any random usermode exploit to launch the kxploit? Ok, maybe not random, but you get my point So once a kxploit is released, it can be backported to earlier VHBL releases?
If that is the case, why are there CEF/ARK releases? I would thing it would be of much more use to the community to not release a kxpolit intill it is patched by sony. Case in point the ones fixed. If Uno was released as a VHBL release, then come 2.05 and the kxploits were fixed, you can release them for Uno. Why would they release a Kxploit that sony doesn't know about, instead of waiting till it is fixed. That way they are keeping a backlog of kxploits, as it were, and people can just update to a kxploit when it is fixed on a newer firmware.
Or, is it just because Sony is so slow normally, and kxploits are not found till they are released by homebrew devs?