Wildfire compared to Alate Hive is a little more volatile and does not destroy any Permanents whatsoever. It's meant to represent a spreading fire as best as possible, and embodies a "Burn" DoT (in some ways) without any counters.
Who has space for more permanents when your junk is on fire? Ain't nobody got time for that!
@Dhanzig: It should be in the notes, but basically you should figure that if you try to Fire Bolt someone with Wildfire or use Explosion on a Wildfire, naturally the fire should spread, Purifying a player through a Water spell or cooling them off with some Ice Bolts might do the trick to control the Wildfire and if a field is flooded, well...