Physics defaults to framerate dependent, because around the time it was first introduced (and this is going back years), people had issues with making deterministic physics. The problem with framerate independent physics is because the time step has small random variations due to timer imprecision, it can result in random variations in physics simulations. This resulted in bug reports like "my tower of physics objects falls down a different way every time". People wanted their physics simulations to be predictable, which is what you get when using a fixed time step, so I (with some unease, knowing the downsides of fixed time steps) changed it to default to fixed. The downside of a fixed time step is, predictably, that it's framerate dependent, so now the physics simulation speed depends on the display refresh rate.
Now that different display rates are more common, the default Physics setting probably needs to be changed back to framerate independent. But now we have the problem of figuring out a way to do that without breaking all existing projects which use the default and rely on deterministic physics.