There's no problem with it not being able to attack planets (1200 damage versus planets would be OP like woah), but rather, one of the audio responses you get when selecting a Orgov anti-building cruiser is "give me a planet to bomb." My response is "I would love to, but your missiles refuse to attack the planet."
I think that it uses the same (or much of) the sounds from the siege frigate, for which the planet-bombing response would make sense.
