Its an established precedent that anyone accused of any sexual impropriety - from harassment to assault and worse, is prima facie guilty, deserves no presumption of innocence, and should be punished immediately.
I think that it's the way the PR statement is written that is 'clever'. By putting the founder on leave and banning his wife from the office they haven taken pro-active action (which was not mandatory). As has been noted, it might seem that they have admitted some wrong-doing when in fact they have not. But it's enough food for the media to drop the issue...
But you at least have to allow for the possibility that they are doing the right thing here. Perhaps they respect Julie enough to take her claims seriously and correct the obvious wrongs (gf in the offices) while doing what every other organization does in putting the person under investigation on leave.
Yes, perhaps they are bullshitting. But this is also what the PR release would say if they were trying to do the right things by all parties but don't have the information they need or the time they need to figure out exactly what the repercussions should be.
But I'm not convinced that this is a "clever PR move" as you suggest. What else can GitHub do at this point? Fire the people involved without even investigating?