It's a financial service, they're covering their ass from unforeseen tax issues. If some people in Russia decide to use it, and paypal hasn't checked to be sure that this is all completely legit under Russian tax law, there will be huge problems for them.
But the argument is that if you can get a PayPal account in Russia, and if you can send money to that account given the existing PayPal user interface, how is this feature different?