It's really unclear what's going on, actually.
We don't know exactly what the FSF is seeing, nor if they did fair tests, nor if they're reporting fairly (though I tend to assume so, tentatively).
We don't know if Google did something deliberately, nor who did it. We don't know how it relates to Per's mailling list message, if at all. If there was action, we don't know if it's an experiment, or a bug, or who it affects, or how often.
More generally, it doesn't seem like this is an urgent issue that requires panicking. The world can get along fine for a month without people being able to invite gmail users. But, on the other hand, if the worst case is true, that Google has started blocking invites from ALL other domains, ALL the time, then I think the FSF's political position is sound.
So far, though, this really isn't like Reader.