The reason why Navighast will not receive Sacred Sword (Theory)

[AgentParadox]

A slight tangent (click)

But there are Kyurem who literally have a ice hand and dont learn Ice Punch and a gastly who dont have arms learn Ice Punch...the irony of the pokemon world I guess.

That isn't irony, it's just a strange coincidence. Additionally, I believe the reason Kyurem has no access to Ice Punch is that sometimes, the Pokémon World does make sense. 

For instance, look at its design:

Notice how weak and spindly its arms look. (IMPORTANT NOTE: Those attachments on its back are not hands, but wings. This explains its ability to learn Fly and Steel Wing, and its inability to learn punching moves.) There are a few Pokémon with small arms that can't learn punching moves, such as the similarly-built Tyrantrum, but I can't think of many others off the top of my head, besides maybe Quilava and Flaaffy. Although true that some small-armed Pokémon can learn punching moves, those Pokémon are generally Fighting-types.



Although Black Kyurem does indeed boast strong arms, the fact of the matter is that it's a forme it is able to switch out of, and thus having the move would make no sense (such as Rotom's inability to learn Flamethrower, Ice Beam, Scald, Aerial Ace or Solar Beam, amongst others). Additionally, it is a host/parasite relationship (sort of), and the host Pokémon is Zekrom, who cannot learn Ice Punch.

Gastly, admittedly, is an odd case, despite how its evolutionary line is built. One can only imagine why a big ball o' gas is able to put 'em up, but such is the nature of Pokémon.

On topic, I think the idea of Sacred Sword actually being Sacred is definitely a very neat analysis and explains why something like Bisharp doesn't learn Sacred Sword as it's generally a foul and nasty Pokémon, though why it isn't given to Gallade (hugely a trainer-protector and a very courteous and affectionate Pokémon) is anybody's guess.