In all the SW games they are always talking about things that happened thousands of years ago, they behave the same way people behaved thousand of years ago... it's like the universe of SW reached a peak and stoped there...
Exactly, Star Wars is set in a fantasy universe with sci-fi elements added. Because of this technological change gets limited from generation to generation. Unlike Star Trek where technology and technological advancement is key to the stories, in Star Wars the overwhelming themes are the battle between good and evil (lightside vs. darkside) and the republic vs. the empire (or whoever happens to be the villain for the story arc).
And I have a question: is it possible for a culture to survive that way for so long?
And even more... we can only talk (for now) of a single planet and a single sentient species... what would happen if we throw a lot of different sentient species and we were to live in a whole bunch of different galaxies, could they all be so much alike?
There have been many cultures that have remained virtually unchanged for thousands of years. The most extensive being China as, internaty, previously mentioned. But there are some Asian and pacific island tribes that haven't changed at all in thousands of years.
Star Wars only takes place in one galaxy, but the different species have had thousands of years to merge into a single culture. Many of the major species have been part of the republic for a long, long time. Some of them keep elements of their "home" culture but for the most part they are part of "the Republic" (or empire).
Nobody put any thought into the Star Wars universe. Some of the tech we uncover in this game is strangely missing in the films so must get 'lost'. So much gets 'lost' that it is just poor continuity.
This is different problem all together. When Lucas originally developed Star Wars he only created a history not even 50 years before the time of the first movie. Since then nearly two dozen authors have written stories set both before and after the movies. Many of them try to create stories as large as the original trilogy and keep adding bigger and bigger weapons or more advanced/exciting technology. By doing this it dilutes the advancements of the original stories. It's a classic case of "too many cooks...." It's evidenced by the existences of multiple levels of cannon. Had only one or two people been given the rights to author books, and only books based on outlines provided by Lucasfilm this problem wouldn't have been as bad.