I can't answer the 600 VDC vs. 750 VDC argument, though I suspect it gives a bit better current flow to the motors so they can accelerate more quickly. Some trolley lines and interurban equipment from the early days even was designed to run on 750 VDC from the factory. In some cases, even the 150 volt difference between designed voltage and current voltage doesn't prohibit elderly unmodified streetcars from modern LRT track.
The pantograph instead of a trolley pole does have some reasons behind it though. First of all, the pantograph wears a lot more evenly and takes longer to wear down than the trolley shoe or wheel. Second, there's no complicated wire frogs to maintain, and no chance that the wheel/shoe will follow the wrong wire path. Finally, the pantograph holds constant tension against a wire a lot more easily, while the trolley pole tends to be a lot more bouncy and less likely to stay in contact with the wire.
On the other hand, trolley poles are a lot easier to manually put up and take down from the wire, and look a lot more graceful IMHO.