You also don't the get programmer comments when you decompile/ deduce. Assuming the programmer actually commented his code (sometimes a big assumption) you get that in open source. Having done bug fixes on code by long gone programmers I know how much comments can help, easily a 50% reduction in "figure out how it doesn't work" (remember I was fixing bugs) time.
Good point. You also don't get the technical documentation that is available for Unix.
I was in a meeting today discussing the Pros & Cons of NT/Win2000 vs. Unix. A techie stated the Microsoft platforms were more vulnerable to intrusion attempts. I had to think of all the Abbie Hoffman's hacker newsletters. These early hackers were all Unix people. They knew Unix inside and out and had the source and documentation to fully exploit it. Of course, their biggest targets at the time were IBM and AT&T.
Now in open source's defense (just to show I play fair, there are people that think I'm an MS apologist and my answer is they aren't complaining about the right parts of MS) because it's open source it's a lot easier for the administrator to change his security and put his own stuff in there; and all the Unix dogs I know do just that. But out of the box I'd have to think that even though on a technical level Unix security is better than WinX security (it is, no way to dodge that) the fact that any geek in the world (including hackers) can DL the code that wrote that out of the box security (and install it and run it through a debugger... all without breaking a single law) has to be considered a big check in the minus column.