Rain of Fire targets all enemy creatures, doesn't hit Immaterial.
Global effects target everything on the field, doesn't hit Immaterial.
Are you saying that because those other cards don't currently affect immortals, no other card should be able to (ever)?
Or are you saying that due to how you think the coding works for global effects, that this type of change might be too much work for the development team?
I'm not sure what angle you're coming from, so I don't know how to respond yet.
Remember: my goal here is to suggest an alternative (better?) way to counter an immortal other than fire shield (which I currently don't like the mechanics of).
This discussion just also made me think:
If you have a darkness or death creature in play, and then play an eclipse, and then immortalize said creature, does it retain the eclipse bonus?
Also, if you have a darkness or death creature in play, then immortalize it, then play the eclipse, does the immortalized dark/death creature get the bonus?