This is the standard, and to me quite unsatisfying, post hoc Expanded Universe rationalization of the error. The more obvious explanation is that George Lucas didn't know then what he knows now after having a bazillion nerds tell him so...that parsec, though vaguely timey sounding, is in fact a unit of distance, not time.
This is not to say that Star Trek is immune from tech blunders or continuity errors...like..how come Worf has red blood while other Klingons have pink pepto-bismol colored blood?
It's just that after 700 or so hours of content...Star Trek seems to try a lot harder and succeeds better at getting the technical/scientific details right.
Probably because Star Trek is much more science-fiction then Star Wars. Star Wars is really a lot more science fantasy then anything, a lot of the stuff in it just /works/ without any actual scientific explanation. Trek at least tries (even if its probably technobabble).