Am I saying that? No, but the GP specifically did.
It only matters when you have something like a monopoly. The issue with Microsoft was that they leveraged their operating system monopoly to create a monopoly on desktop office software, and part of the way they did it was by using secret, private, undocumented, proprietary, whatever you want to call them, APIs or features built into Windows for Office. A company is not allowed to give itself an unfair advantage when they have a monopoly to spread to new markets. That constitutes abuse.
Not sure about your question about private functions, because that’s a feature of OOP and not really relevant.
When Microsoft comes out with a new version of Office that works with a brand new version of Windows using features of their competitors did not know existed, I think it’s pretty obvious why their competitors are unable to have a product on the market in a timely fashion using those functions. Again, that’s only relevant if they have a monopoly on a market. Of course, a company is not otherwise required to help competitors do anything.
See: http://lowendmac.com/2008/rise-of-microsoft-monopoly/
“I have decided that we should not publish these extensions. We should wait until we have a way to do a high level of integration that will be harder for likes of Notes, WordPerfect to achieve, and which will give Office a real advantage . . . We can’t compete with Lotus and WordPerfect/Novell without this.” - Bill Gates, 1994