If the market pays lots of money for Mac OS X exploits, why would it pay less for Windows ones? It can't be market share and I doubt it is because Mac users have faster Internet (so that their machines can be bigger DDOS sources, have more money to steal from them (both may or may not be true, but I doubt that fully offsets the difference in market share)
Another only thing I can think of why Mac exploits would be more expensive is that buyers expect Mac zero days to last longer, but I doubt that, too.
That leaves two reasons: because it is so easy that nobody considers it a challenge, and everybody expects someone else to pick up the price, or because it is too hard.
Alternative theories welcome.
Some theories:
I don't necessarily think it's because Mac 0-days last longer, but I know they do consider it a challenge; The difficulty may factor in to the price somehow. Maybe because there's the presumption the average user on iOS may have more cash to burn than the average Windows user.
They may have more to gain by hitting Apple employees for trade secrets.
Of course, all this is pure speculation.
Safari on OS X is considered a soft target compared to the other browsers. It is the least difficult and has the fewest users. That is why the payout is less.
It has nothing to do with being after trade secrets from Apple employees. The people who sell both iOS and Mac (OS X) exploits do not sell them to people trying to steal Apple's trade secrets.
Pwn2own bounty for breaking IE9 is only $75,000.
Bug price list 1 year ago:
http://www.forbes.com/sites/andygreenberg/2012/03/23/shoppin...
It is indeed too bad that the Safari bounty is only $65,000.
And IE9's bounty is only $75,000.
So yeah, perhaps these bugs are being sold to governments instead.