Well, who knows ???
It's an unfortunate situation. I don't have any doubt regarding Venus' injury (she looked committed to the game at AO and devastated when she lost), but I have some problems with Serena's withdrawals or at least her statements. I just don't believe she's "daily on the court practising and fully fit" like she says. It MIGHT be true of course. But then why isn't she playing tournaments already ? Either she's not willing to travel outside the US for just one tournament, or she just isn't really interested in tennis right now, which is what I tend to believe. Again, I might be terribly wrong.
Either way, it's a disaster for the game that both are out for such a long time while most people still see them as the top-contenders, which in one case might not be the reality.