OK let's preface this with the obvious.
First, we know that Smoltz is coming back to the big leagues soon.
Second, we know that we have a strong, deep, effective bullpen.
Third, our optionable players -- Masterson, Bard and Green -- are all filling vital roles, and the only one of the three you can afford to send down right now is Masterson, which only makes sense if you still see him with a future in the rotation and want to get him stretched out.
Fourth, Saito is an older veteran signed to a short-term deal, and of all the men in our bullpen right now is the one the team is committed to the least. Also, having proven himself effective and healthy, Saito's trade value now goes up based on his reputation and possible value as a possible closer for a team in contention.
In other words, trading off a pitcher is a move that makes sense to clear space for Smoltz. With Delcarmen, Ramirez and Bard all looking solid, effective and durable we could afford to give someone like Hunter Jones a second shot without destroying the bullpen if it doesn't work out. Rather than making a move based on a player whose value is low, like Daisuke or Penny, hows about we trade a guy whose value is about as high as it could be under the circumstances? I guarantee we get a better return for Saito than for Penny, and I doubt I get much disagreement there. A guy with closing experience who's proven himself healthy and effective? Yeah, someone goes nuts for that -- Texas is a great candidate for example.
Personally I don't know if it's the perfect move, but it bears all the hallmarks of a good move, and might be the right move for the team.