Coach here again...lots of good point made here. At the younger ages, some players are the stars because they just happen to be bigger or faster than everyone else, some because they are truly better. Obviously without seeing the tryouts, I can't tell you specifics of why someone didn't make it. Is travel soccer pointless for young kids because you have no idea what will happen physically after puberty? No, because so much of being a good player is mental.
Keep in mind though, that the US in general is terrible when it comes to developing soccer talent. Most "real" soccer countries think that our method of "pay to play" travel teams, to high school, to college is a terrible system...most countries leave it up to pro teams to discover talent early and train them as they see fit. Check out this really interesting NY Times article for one example:
http://www.nytimes.com/2010/06/06/magazine/06Soccer-t.html
But since more people here are probably concerned about college scholarships than building a pro, I would recommend starting in travel as soon as possible, because, for better or worse, that's the best way to climb the latter to the premiere D1 teams.