That's a very basic error, but I can't offhand remember coming across a story where the author made this mistake. After all, if the ship's top speed is even modestly below light speed the journey really could take many decades. Can you give an example?
I wasn't referring to the author in the article, but rather an unspecified collection of 'popular' SciFi, where this aspect is not explained. It is true that, even if you reach speeds of 0.5c you only get a ~15% time dilation.
Which is why most popular sci-fi franchises end up with velocity caps, justified either in-universe or out-of-universe. E.g. Star Trek sublight propulsion (impulse engine) has been established indirectly and through "word of God" to work with speeds up to ~1/3 c, which is not enough for relativistic effects to cause a big impact. The issue is conveniently omitted, because why travel fast through "normal space" when you have easy access to warp drive / jump drive / hyperdrive / wormholes, that gives you FTL and happens to drop you out into a convenient reference frame? And all the interesting action happens around planets anyway.
This omission makes it easy for the writers to introduce relativity as a nerdy plot point. For example, StarGate: Atlantis had an episode with a ship traveling absurdly close to the speed of light, which was devised as a convenient way to introduce characters that should've been dead for many thousands of years.
