No, that's related to writing kernel modules. I'm talking about writing propriety apps on a gnu/linux distribution, android in that case. This is totally legal

No, that's related to writing kernel modules. I'm talking about writing propriety apps on a gnu/linux distribution, android in that case. This is totally legal and doesn't depend at all on the kernel license exception. Think skype on ubuntu. However, if the toolkit/sdk you're using on a gnu/linux distribution is GPL, then all your apps will have to be GPL, unless you use a non-gpl sdk or write your own non-gpl sdk as Google did.