1. I'm not sure on the situation in Russia, but in the US, a lot of teachers don't know much about Windows or OS X either, but unless something breaks they wouldn't have to.
2. Gnome's memory footprint is rather large, sadly. Depending on whether the Russian authorities roll their own custom distro or image though, they could use XFCE instead.
3. As things move more towards the cloud, I think that kids would mostly just have to learn how to use a web browser. Those are mostly the same on all modern platforms.
4. Having to learn something new is not a useless skill. Being able to use more than one platform demonstrates the ability to adapt to change. That's a useful skill to have.