With Linux and Windows people expect to shove in anything and it to work, but that isn't the case 100% of the time, why give the impression you support 100% of the market when you don't?
Buy an iPod and we all know we must use iTunes. Buy an Xbox controller and don't expect it to work on a PS3. Buy a Parker refillable ink cartridge, don't expect it to fit in all other fountain pens.
It's the way the world works at the moment, like it or not.
Microsoft does it, Apple does it. Even Linux does it with their awkward licensing, want to use DTrace, ZFS, or pretty much anything that comes under the CDDL or BSD license? Oh sorry, the GPL license forbids developers to add it for distribution, so unless you want to compile your own kernel, you're stuck with running things in user land.
Unless we all give everything away for free, it's not 'fair'. Proprietary systems are always going to exist, they may have large parts of open source code in them, but there will still be large chucks of proprietary code. And then there is the fact that people don't just want to give things away.
In these instances, if you don't like it, don't buy/use it.