Nothing at all has changed in the real universe out there.

Just some things in human's brains.  And a whole lot of media airtime...

Realistically, they've recently discovered a whole lote of beyond Neptune objects, if Pluto is a planet what about them??  So they've tightened up the definitions.  In reality a single word Planet that defines Mars and Jupiter is a bit of a joke.  Terms like Gas Giant are a whole lot more useful...