Russian players are very tall and have long arms, IMO that's where their advantage got from.
I'd add Isaeva to strong server list, she has got some outstanding arm swings that in general we don't see very often these days, many erros can be made, but still entertaining. Also Samoylenko is a good one, just like Fetisova. I don't think she even targets somebody, however the opponents hardly take them.
Agree about Sasha and Zenya, especially Sasha improved a lot and turned out to be a strong server.