Seems like a reasonable decision from NZF.
Agreed, I'm a bit dubious about the NZ Under 20's, but they are likely to be more competitive than Manawatu, and it's not like our league is a superbly-regarded professional league so I don't see how they make a "mockery" of it.
Nelson wouldn't have won too many games, nor Wairarapa, and three Auckland teams out of eight would have been too high a ratio for my liking. Though, as long as I can keep attending Waikato games for the next three years I'm happy either way.