Apart from the theory that some on the fence gamers may drop 20quid or so to try it (xbox also has a 1 hour demo), i can see other logic in selling the base game alone.
The base game is a deep game in its own right, and the learning curve is steep. Expecting more casual gamers to stick with the game longer term with all the Horizons content as well to get their head around from day one is a slight risk - they may get put off the game real early, and bad word of mouth could hurt sales long term.
However, if you can pull in more gamers with the cheaper base game option at the start, and offer a dlc path that adds a lot of extra content at a great price, while extending the learning curve, that can only be good. It's a better way to encourage longer term players, which will keep the galaxy alive.
And, if its not out before e3, expect the frontier presentation to be "welcome to e3, here is elite dangerous on ps4, which you can download from the psn store straight after this presentation by david braben".
And then keep an eye out for the braben bobblehead to make a limited comeback
