Back in August the Crawfish Boxes posted a recap of a meeting between season ticket holders and Astros president Reid Ryan which, in part, addressed George Springer's Leave-Down (as opposed to "Call-Up"):
The FO expects the team to be a big Rule 5 target this year and so they
need to protect as many guys as possible. Since Springer isn't Rule 5
eligible yet there's no need to protect him and therefore, no 40 man
spot until next year.
Farmstros' Mike Tauser got a question in to Baseball America about this very topic: Do the Astros really have to worry about getting Rule 5 picked to death?
In reality, the Astros are not facing a 40-man roster crunch. They have
the deepest farm system in the minors, but most of the players worth
protecting won’t become Rule 5 eligible until 2014 and beyond.
Basically BA is saying that the players the Astros "need to protect" won't really appeal to other teams...not enough for them to stick on a 25-Man roster for the entire 2014 season. Next year, though...