Did you never hear of the Free Software movement? The closed, or non-free nature of Windows was one of the prime motivators for lots of open source projects. See https://bugs.launchpad.net/ubuntu/+bug/1
What was closed about Windows was the source code for the kernel as well as libraries and APIs. As a very strong supporter of Free Software, this was a huge part of what I railed (and still rail) against.
In terms of the ability to run random bits of code on it, Windows was highly open. Perhaps too open when you take into account not only malware, viruses, and spyware, but the various crapware/bloatware OEMs would pile onto their Windows preloads.
Arguably some Linux distros, with their comprehensive archives, though with rules for what could or couldn't be installed (based on licensing requirements) were more "locked down", though in truth you're more than open to install third party from sources, as binaries, or any other means you care. In practice, I prefer sticking largely to my distro's own archives and installation tools, precisely because the software is both more vetted and generally behaves far better.
it was a closed system... I remember my dad shelling out $500 for MS Visual basic for me, and then $500 for MSVC++. Visual basic was fun, but I didn't do anything with it. I never got past MFC in VC++ and I wound up using borland's C++ instead for my science fair project.
Now, I can put ubuntu linux on my machine - for free (or in my case, preloaded from DELL at a discount over windows) and get a million different toolchains with free documentation online.
a fair criticism. It was de facto closed. Keep in mind during the 90s, the internet was limited (for quite a bit of that time I didn't even have a 2400 baud modem). It wasn't until my second year in college that my friend introduced me to linux, and I still didn't actively start using linux until 2006-ish (I spent 1999-2003 in BeOS and 2004-2006 in FreeBSD)
i guess the part of my complaint that had the most to do with 'closed' was the MFC/developer licensing part. I knew enough to know there were APIs lying underneath that weren't exposed to me that I could do awesome stuff with if I was able to see it. At least with BeOS it "felt" like the most important part of the API were exposed - and with linux I know that they are in principle, even though I never use them.
There are plenty of free and open source toolchains and languages for Windows... in particular the same ones available on your Ubuntu installation (gcc, openjdk, python, etc.).
Microsoft sells and supports development toolkits, and they happen to be better than a lot of the free ones. I bought PyCharm for Linux -- that doesn't make it closed.