About OS/2 apps and Windows security
It is not really true that Lotus, Ashton-Tate and WordPerfect focused on OS/2. They yes, released something, but was little of of poor quality. I bought in 1994 a PC with OS/2 3.0, and found myself using Windows 3.1 applications. The promised Lotus Smartsuite for OS/2, for example, never materialized. And the Windows version was really ugly compared to MS Office 6. Without applications, and with some rough edges still, OS/2 was doomed despite some nice features.
Windows started to become a much more secure system since Windows 2000, if users and especially developers had started to use it the proper way. The real mistake was not to enforce it since the beginning. I still see developers using Vista and 7 stubbornly trying to bypass security to write in protected directories, just because they don't want to change old habits. It is true that a lot of businesses relies on a lot of old, bad written code, but MS should really start to enforce security instead of hoping end users will understand it. Apple had the advantage its user have not those large heritage of legacy applications to run.
But although the spotlights are on web or mobile apps, your desktop OS is not going to go away anytime soon. My guess is that in 25 years there will be still a Windows on your system. And when mobile device will become more powerful, they will ditch limited OSes and move to full ones supporting much more features.