Although MS may fork something, it does not force you to use their proprietary language - In the examples above, you can still use the original language...the choice remains yours.
I might be biased since I've basically only developed on Windows (Visual Studio, code warrior, borland, etc.), but in the big scheme of things, MS has been more open, had more alternatives and options and better developer support than Apple...IMHO.
As anyone that has had to write parallel code in HTML/CSS/JS for IE vs every other browser your choices are: do it our way.
MS was only open in their willingness to assimilate other good technologies, and then lock everyone else out once they had enough influence.
Or was "Thoughts on Flash" intended to be Jobs's pitch for Core Animation?
There are open source alternatives like Gnash but they are reverse-engineered runtimes. And like all RE'd apps they are at the mercy of Adobe. It already has problems with Flash 10. This is why Jobs argument is so valid. Anyone can write a swf file but it's restricted to running on Adobe's Flash runtime.
PDF is a special case. I still have an Acrobat 1.0 disk in storage with my Photoshop 3.1 floppies, somewhere. Adobe was giving it away at that point. They also gave licenses to PDFs. Only one company took the offer, Next. Apple bought Next and inherited that license from '93.
For Apple to be like Microsoft it would have to take a standardized language (like HTML, Javascript, or Java), fork it so it is unreadable by the original, then use it's monopoly so that no one else can create a competitor.
Here is a rundown of this MS behavior:
MS-DOS vs. PC-DOS
J# vs Java
IE6 vs HTML4
MS JS vs javascript
Now when Apple forks Flash and decides that is the only Flash that will be available on iPhoneOS then they will have become Microsoft.