I'm pretty sure this design decision dates back to first edition, but i havent dug out my book to check. I know it was there in second and third and fourth, and i'm pleased to see that its still kept this way in 4A.

I think its great how the spirit details listed in the Critter section say nothing about spirits immunity to natural weapons, and that you have to have read the conjuring rules in detail to know about it. it really helps you seperate out the people who know shadowrun, and those who dont. lets you know right away who has read the rules and who the n00bs are.

even though the world has changed and immortal elves and ED tie-ins and reactive triggers and calcify spells have come and gone and maybe come back again over the last 20 years, its good to know that some things are still the same as ever.

It's because the spirit only gets the power when it Materializes or Possesses; it isn't a power they always have. It's clearly listed in the write-up of the Materialization and Possession powers.

seems rather irrelevant, after all, if something is hitting a spirit on the astral, it obviously isn't a normal weapon is it? And therefore the ItNW wouldn't apply anyway even if it did have it.

wow, its been hidden under materialization all this time. who'd have thought.

it's theoretically possible. if spirit A is materialised and a great form guidance spirit puts the area including spirit A into an astral rift (or any other area which causes things to become dual natured, etc) then a normal weapon could indeed be used to attack that spirit. because it is materialised, it would have immunity to normal weapons active, however. (in comparison, if it was not materialised it would have 3 IPs even to affect stuff on the physical plane, but no ITNW)