Sure - for openvz it was more powerful resource accounting and limits (this is back in 2008). I think there was extra goodness around networking, but honestly I can't remember. Mostly we were trying to figure out which project would find its way into mainstream, so we could standardize on that. vserver had been around forever and somehow never made it in, so OpenVZ looked like our best bet. Of course we turned out to be wrong :)

There's a related discussion here: https://news.ycombinator.com/item?id=6227937