Why is everyone worried about unlimited?

Flame of Reincarnation.

That you can't get unless you can kill the corresponding boss that dropped the gear you have in the first place, from my understanding.

Which means if you want to add AO to your Empress gear, you're fu'cked until people have spent enough to finally be able to deal with her again, and you certainly won't be able to do it yourself, or even with a group of friends unless you're all spending way too much money.