there are always tickets available on the day, even in the afternoon, though not always for the show courts. u can buy scalped tickets from touts outside very easily (last year the checks were minimal, not like wimbledon with their wrist bracelets and all!!!).
Let's just put it like this, there is Justine Bieber (I just threw up a little) who ... is hyped far beyond his talent.
Then you have Michael Jackson & that name speaks for itself, no hype needed at all.