I believe this is incorrect. The server usually listen on one port, but everytime it does an accept, a different random port is used, and the client start talking to the server on that new port.
And yet there are a lot of active exploits targetting Windows. If your logic was sound, given that Windows is by far the most used system it should also be the most secure: then again I invite you to research the subject, security reports often show that it is more vulnerable than most linux/unixes. I find 7 to be an acceptable OS (and I still use it everyday) but blindly beliving that Microsoft ecosystem is secure because it is Microsoft's is a mistake.
"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.
I do agree on the fact that it is totally embarassing for Dropbox, and I do not either recall a similar issue with Microsoft, which does not make it safe. DEP / ASLR mechanism have been "easily" bypass several times this year, which to me is also embarassing. But the fact that this issue happened with Dropbox does not mean that it will again, and I'm pretty sure that it will make security one of their top priority. I do believe that going to Microsoft for better security is an odd move.
I happen to use 7 / archlinux / Os X almost equally. Of course my comment was trollesque, but an affirmation like "Microsoft ... tends to be very good about security updates" is not realistic. Time elapsed between exploit discovery and patch proposal to the user is everything but short. And If every website with a security issue was to answer to the congress, well it would not do much else. Plus, given the money Microsoft spend lobbying, I doubt very much that in a similar situation they would have to answer to the congress. Dropbox just seems to be a marked man.
To me, going to Microsoft for security is like going to the desert for ice-cream. The article seems quite biased, since "embarassing security failures" tend to happen more often at Microsoft.