The math bit is about right, the rest is bullshit. I implemented a 2-way satellite modem, with VoIP, a few years back, and 600ms RTT is what I got typically. Upstream bandwidth contention is handled with QoS on the link layer and some form of traffic shaping. After that, from the ground station, it's just a fast link to the Internet like from any ISP, which means roughly 150ms to get across the Atlantic, for example. So real-life ping times are well under 1000ms.
The Slashdot crowd seriously underestimates how much engineering goes into modems to ensure that the end user experience is optimal.