I think Pentadact said it best on QT3 *spoilers*:
"I see the Princess as a symbol of unattainable obsessions, almost unattainable obsessions, and attainable but regrettable obsessions. And a lot of Braid seems to be about what that obsession costs you, what you can get back and what you can't.
The Stars seem almost like a joke on that, showing obsessive gamers just how lost to their quest for completion they are. It's virtually inconceivable that anyone would find that overworld star before they finish World 2, so Braid forces you to sacrifice all the progress you've made to earn just one more empty accolade.
It works both as a "You never get the princess" fable, and as an
"Actually, if you're really fucking obsessed with it, you can reach the Princess. But Jesus, look where it gets you and what you lost. Three hours waiting for a fucking cloud. What's wrong with you, man?" fable. A niche genre of fable, but a worthy one."