True. But if you do it over a long period... TOR has been around a while now. How can you possibly vet all owners? Surely most relay owners would prefer to remain anonymous.
Yes, I'm sure there are relays being run by the NSA and other governments. But people monitor the creation of new relays an attempt to determine who is running them. It's not a simple task to fool everyone.
Since a large part of initial Tor development was funded by the US Navy and then DARPA, I think it's a safe bet that the NSA et al. have been doing this ever since the first public release.
