Not as many as you would think.
A few years ago, before the whole UIGEA thing, I had the rare oportunity to see the stats of a guy who held the top 3 spots for those keywrds and although I won’t disclose a number – I’ve got to say I was pretty disappointed.
Today with the troubles depositing, the money most of those guys spend to keep their positions, etc. I don’t see those keywords as top priority. Don’t get me wrong, it’s still a very cozy place to be, but you can easily get very close to their number of players by simply targeting niche keywords and without spending a dime.