(I'm assuming those lines are looking up a specific itype, not a specific item)
Because that would convey the incorrect notion that item_controller is simply a collection of itypes. In addition, from the several hundred I've looked at none of those places have any real business requesting itypes to begin with, and I plan on replacing every single one of them with an appropriate implementation by the time I'm finished. The only things that will know or care about itypes when I'm done are the various item instances (which will use the itype for default values) and the item_controller (which will use the itypes to create and return the appropriate items).

However, as an incremental change, it might have merit. I'll look into it.