Ah, Special Relativity...
"The big snag with worlds orbiting other suns is of course that they are utterly, ridiculously far away and according to the laws of physics nothing can travel faster than the speed of light: meaning that journeys even to a few of the nearest stars would take years at the absolute minimum, and in general interstellar voyages would simply not be on human timescales."
Erm, I don't think that's quite right. Timescales are only a problem for those left behind. Although under Special Relativity it is not possible to exceed the speed of light, those approaching it experience time dilation under the Lorenz Transformation relative to those stationary. So at relativisitic sublight speeds, journeys to other stars don't take millennia *for those on the journey*, although a "mission control" back on Earth would experience those timescales.
Sure, there are still issues with the time it takes to accelerate to relativistic sublight speeds at a rate that doesn't squash crew to a pulp (and turn around for deceleration so as not to go shooting past your destination). But even with very modest accelerations, the relativisitic savings can be huge: for example, a journey from the Sun to the galactic core using just 1G could take just ~340 years for those aboard, compared with ~30 000 years passing back on Earth. And at 10G, it would be ~110 years.
So if you want to get to the stars, it's perhaps not quite as difficult at the text of this article suggests If you want to do so while keeping a culture intact across the stars - well ok, that's much more tricky unless you can get round Special Relativity.
The notion that "it takes X years for light to travel X light years" is erroneous; in a frame of reference at the speed of light, time dilation is infinite, i.e. there is no time in a photon's frame of reference (and there's no distance either, thanks to infinite length contraction, i.e. photons don't actually "travel" anywhere in their own frame of reference). Didn't you watch Carl Sagan's Cosmos as a kid, Lewis?