I’m not sure about the “selctive” part other than, as you say, avoiding what sounds like sending the wealthier people to war. They’re using mercenaries (or at least foreign “voluneers”), conscripts that force Ukrainians to fight their own people, jailed criminals, pretty much anyone they can send that doesn’t have enough clout to cause a stir. Plenty of russians have fled the country that could afford to do so, and more will follow.