Secunia finds out about most of these because APPLE tells them because they are, for the most part, open source. How many things has Microsoft quietly patched and never mentioned, because they are considered "trade secrets."
Several times, when Secunia released its latest FUD, I have analyzed their exagerated "security levels" and found their hysteria totally unwaranted.
Anybody who says XP is more secure that OS X has been licking toads or getting a paycheck from Redmond.