This has been brought up time and time again, and here's how I stand:
Cards immortalized with anubis or have immortality adherent to their card can not be targeted. Make this ability "Immortality."
Cards immortalized with quintessence or aether nymph can be removed by another card (such as this one. I like this one). Make this ability "Immaterial."
The ability names I don't really care about though. It's more of the effects I would like.