I think with the encounter at farpoint mention that would indicate cbs wants to start with season one if they are doing all seasons. It would take care of a double episode. It would have the ilm effects of the ent-D shots. It would introduce the show to people who have not seen it in the same way it was introduced in 1987.
4 episodes is an investment and not a full season of investment just yet. Maybe they want feedback. Maybe cbs wants to find out if in-house is the best way (err most cost effective) to go?