If you were to create the perfect unexploitable operating system then you would, in effect, be putting yourself out of business...having eliminated any reason for repeat or justified business.

Now...I'm not suggesting that Microsoft could create a perfect operating system...what I'm suggesting is that they don't even try to...exploits like the one below not only justify their existence but give cause to spend the money to upgrade thus creating the good business practice of repeat income.
Microsoft late Wednesday warned Windows users that proof-of-concept code was in circulation that could be remotely and anonymously exploited on Windows 2000 machines. Windows XP SP1 is somewhat less vulnerable, said Microsoft. The security advisory gave out few details of the vulnerability, only saying that it was a flaw in the RPC (Remote Procedure Call) component, and could result in a denial-of-service attack that would crash affected computers. "On Windows XP Service Pack 1, an attacker must have valid logon credentials to try to exploit this vulnerability," Microsoft said in the advisory. Windows 2000, however, can be attacked remotely. That aged operating system has been victimized by several vulnerabilities which have singled it out for attack since mid-year, including August's Zotob campaign. Windows XP SP2, Windows Server 2003, and Windows Server 2003 SP1 are immune to attack. As far as Microsoft knows, there have been no attacks of the exploit, but the whole matter is under investigation. It may release a security update to fix the flaw in the future, the company said, though like always it wouldn't commit to doing so.
http://www.hackinthebox.org/modules....icle&sid=18525
Microsoft Warns Of New Windows 2000 Exploit :: Hack In The Box :: Keeping Knowledge Free

By creating an unexploitable system you in effect kill any security-related reason to upgrade...you may still be prompted to upgrade for better/newer software upgrades, etc...but the main focus to upgrade would no longer be viable.

This all begs the question : does Microsoft purposely. in veiw of it's own future, create exploitable systems, or even, as the authors of, create the exploits themselves, to justify itself, and ensure upgrades and renewable income?

Eg