When using some open source softwares in the company, we usually try to change some parts of them. Like bootstrap(index file), the way processing password or connection and maybe include some private work-flows and put 'Winnie The Pooh' in the front-end. Then we could get survival from the attacks if they don't know the modifications we made and the people won't know we had done some stupid things besides the users in the company.
I was not talking about the traditional way that proprietary software vendors did. Most of web based open source softwares are using GPL license and they had gotten big successes like joomla, as bruzergear mentioned, and drupal, xoops, sugarcrm,...
If I said AGPL is a kind of communism in web based software, maybe GPL is something like tax in capitalism. There always exists people who try to argue some other people doing evasions of tax, but it's not the reason we should choose communism.
AGPLv3 for web based softwares is not the same case with GPLv3 for desktop softwares. For example, if somebody had a software being setup in his laptop. You borrow the laptop and use the software. In GPL, you can't ask the source code of it if somebody haven't released the software to you. But in AGPL, you could ask the source code since you could access it.
And in Micro$oft case, they sure won't release the source code in your view point. But the developers and vendors around the software licensed in GPL they are using, they have the rights to get the source code of it if they don't want to co-operate with Micro$oft, and they also have the rights to release the code to community. That's why Micro$oft won't use any softwares which licensed in GPL in their business.