All good answers. I can't fault any of them.
I suppose my irritation regarding this is when people talk about the limits of a pure mortal. it seems to me that there are very few (pure mortals) within the system then; at least from a playable standpoint.
I always had the feeling "Pure Mortal" had more to do with supernatural heritage and free will than carrying a magical item. Though if we're simply talking refresh spent on powers then I suppose I can't argue hte definition.
However, when commnents or arguements are made that a pure mortal cannot fight a loup garou or something, people are likely only refering to people with just stunts; no IoP or powers.
I would hazard that a Knight of the Cross is only better equiped to fight a loup garou offensively, becuase he/she is no better off defensively. The arguement or comment is then flawed greatly.
I think that you're thinking Items of Power too much like simple magic items rather than huge deals. I mean to even wield an IoP your character must have an aspect representing it, so already by their very nature that are eroding your narrative control over your character. Lets look at a few examples that we're likely all familiar with.
The One Ring: When Bilbo had the ring over time it drove him insane with paranoia, when Frodo was given it he had to go on an epic quest, these both sound to me like loss of narrative control.
Excalibur: When Arthur was granted the sword it became one of the defining features of his rise to power.
The Swords of the Cross: (yes I know, but fictionally we can look at them separately) No one who wields a Sword of the Cross does so lightly, to take up the burden means to take up a great deal of responsibility, which is why when offered it is not taken up lightly.
Personally I have a tough time coming up with an IoP scale thing without it seeming to be central to the characters fiction, and since Refresh represents not having control over your characters destiny it seems perfectly appropriate for them to cost your characters Pure Mortal status.
It's also fair to note, since this may just be a terminology divide that we're having that having an IoP makes your character no less pure mortal. Killing Michael would still be bad for a Wizard for example, the only mortalness that your loose from taking an IoP is the 2 free refresh (which interestingly may just be absorbed that the IoPs refresh bonus).