A long time ago from when? If it was a long time ago from a point that's a long time in the future, the Star Wars Galaxy could be our own galaxy in the distant future. Basically its another way of saying "Once upon a time".
The phrase "A long time ago, in a galaxy far far away" is George Lucas' way to mean "Once upon a time". But taken at face value, it's obviously a long time ago from the time it's being told: now... or rather 1977, the year SW hit the theaters for the first time.