Something like that, yes.  The basic assumption I'm making is that it works like Spell Immunity (http://www.d20srd.org/srd/specialAbilities.htm#spellImmunity), save that it works on 'all magical and supernatural effects', rather than merely those that allow Spell Resistance.<br/><br/>Since Spell Immunity is like having SR: Infinite and SR allows a creature to be affected by its own abilities without having to be lowered, the logic then follows that the Demilich can be affected by its own abilities and those spell effects listed as affecting it under its Magic Immunity, and is otherwise immune to everything else that isn't an Extraordinary ability.