There is no 4.20 DEX pup on the wiki simply for the fact that we do not have our hands on it. It was not deleted and there is no conspiracy with devs not sharing it, we just don't have it yet.
It will be there when we have it. http://www.ps3devwiki.com/files/firmware/OFW-DEX/
I am not a developer. That doesn't mean I don't know what i'm talking about.