Yes there is a time between discovery and patching but if you look at their competitors, Windows is much farther ahead in the security realm. Microsoft's whole security cycle is better defined and IT managers have a much easier time managing security updates from Microsoft than anyone else.
Dropbox isn't a marked man because it doesn't have the capital of Microsoft, they've had to testify because they have a serious security and privacy problem.
"if you look at their competitors, Windows is much farther ahead in the security realm" and that of course is not heresay but solid facts. If you exclude linux, bsd distros, and solaris of the "competitors", then you may be right. So far most of the securty / pen tests reports I have read (and my personal experience demonstrate) that it is way more easy to penetrate a Windows system than a unix / linux one. I like this sentence "There tends to be a lot of myths about Microsoft security particularly in the non-Windows using community" because the symetry is interesting: most non-unix/linux fail to see that these systems are usually more secure. I have used both kinds for 10 years and had much more security problems with Microsoft (which does not mean that I have stopped using it). I do not believe I am the exception.
Dropbox isn't a marked man because it doesn't have the capital of Microsoft, they've had to testify because they have a serious security and privacy problem.