For complete clarity:
Sins vanilla was released in 2008.
Sins Entrenchment expansion was released in 2009 - that added star bases and better defensive options.
Sins Diplomacy expansion was released in 2010 - which added, well, diplomacy.
Sins: Trinity is simply the name for vanilla and the two expansions in one package, as it was released on Steam in 2010.
Sins: Rebellion was released this year and is a stand alone expansion which splits the three races into six, adds massive titan units and nippy corvettes, and brings the graphics engine well up to date. Steam only.