It makes plenty of sense.
The Trials are in fall 2007.
You let proven talented distance runners debut at the marathon Trials completely oustide of their track season.
This allows them to develop on the track in 2007, have a crack at making the marathon team and then focus on the 2008 track season if they don't make the marathon team.
If they make the marathon team then that certainly proves their marathon ability and allows them time to train for the marathon for The Games.
There is no need to do this for track events since you can frequently race the other events without really bothering your training/racing scheduling.
I don't see how this undermines the marathon as an event. If you want the qualifying for the marathon Trials to be so precious then lower the standard to 2:15 to be in line with the other events.
I am in favor of the current set up that allows greater participation but still has some level of difficulty to get in.