This has been sitting idle for a while, but I came back upon it just now and happened to notice a similarity among the organizations listed in the Q. I would have just made it a comment, but it's too long. And having converted it to an answer it got even longer for completeness. Maybe it does help you understand what's being asked about, though.
Ignoring the WTFPL which doesn't talk about revocability because they are basically a wordy way of saying "This is Public Domain".
The two organizations that don't say anything about revocability have large staffs of lawyers, who write all their legal stuff; usually for B2B licenses. The others have 0 or 1 lawyer and are mostly concerned with end-user (i.e. consumer) licenses. I understand why this distinction between them results in the different language.
That understanding comes from having worked as support staff at MIT and having talked to one of the MIT licensing lawyers about some code I wrote to do my job and my desire to distribute it with a GPL license. At one stage the MIT lawyer was all set to allow it but with one final question, he had no idea what the phrase "TO THE EXTENT PERMITTED BY APPLICABLE LAW" (which at the time only occurred once and in all caps, now there are several variants in several places) was there for. To his mind having it there meant that the reverse might be true without it. But you obviously can't grant something in the license that is not "permitted by applicable law". So what was it saying? Well, the answer (from FSF's lawyer) was that this was standard required boilerplate in licenses to consumers who are not expected to realize this exemption and have lawyers to research it for them, whereas the MIT lawyer and all the company lawyers he deals with are such lawyers. There was case law (in the consumer realm) that a license without that disclaimer can be dismissed wholesale as an illegal license. Or more accurately chopped into little bits and discarded that way. And, since I was putting it up for FTP (it was pre-web) publicly on the net meant that the consumer oriented text was the right thing.
I expect there is a quite similar story behind the correlation between the irrevocable terminology and the organizations that included it. It may well be one of those case law in the consumer realm but never in B2B licenses differences. In fact, there may be a strong correlation in licenses that have one phrase also having the other.