Consider these facts: Damon's biggest financial hits, in chronological order, have been 'Good Will Hunting' ($138M), 'Saving Private Ryan' ($216M), 'Ocean's Eleven' ($183M), 'The Bourne Identity' ($121M), 'The Bourne Supremacy' ($176.2M), 'Ocean's Twelve' ($125M), 'The Departed' ($132M), 'Ocean's Thirteen' ($117M), 'The Bourne Ultimatum' ($227M) and 'True Grit' ($171M).
With the exception of 'Good Will Hunting,' you could make the argument that Damon wasn't instrumental in any of those films becoming successes. He's the third lead in the 'Ocean's' franchise behind Brad Pitt and George Clooney; he doesn't factor in 'Saving Private Ryan' until the third act, despite being the titular private; 'The Departed' and 'True Grit' are ensembles that don't necessarily reflect Damon's singular star power. Only 'Bourne' stands as a testament to his solo box-office bona fides, and even that could be questioned. After all, did Damon make 'Bourne' or did 'Bourne' make Damon? (This question will get answered next August, when 'The Bourne Legacy' with Jeremy Renner arrives in theaters, sans Damon.)
This is not to say Damon isn't (A) one of the best and most likable actors of his generation and (B) a "movie star." For one thing, he stars in movies (duh, but still); for another, films like 'The Informant!' ($33M), 'The Adjustment Bureau' ($62M), 'The Good Shepherd' ($59M) and 'The Talented Mr. Ripley' ($81M) would have never done as well as they did without Damon's face on the poster. It's just that comparing Damon and Cruise seems specious at best -- especially when even Cruise's recent "bombs," 'Knight and Day' and 'Valkyrie,' earned over $200 million worldwide.
Think of it this way: if 'We Bought a Zoo' had starred Tom Cruise, would it have grossed more than the $13 million the film earned with Damon at the helm over Christmas weekend? (Put another way: is it any wonder that Tom Cruise is behind Cameron Crowe's biggest box-office hits?)
So, no: Tom Cruise and Matt Damon are not "starting to switch places." They never switched to begin with.