If the spell is cast, but absorbed by the item rather than having its effect around the spellcaster, then it would have the exact same effect as if the spell just left the casters memory (or the slot just went away).
True, the end result would be the same -- except that unless you Rule-0 your game, that's not how it works. It's actually stated that the spell is not cast, just removed from memory as if it had been cast. So while the end result of what you say would end up being the same, the method that you use to create the item is different from the core rules.
So unless you tell me that you are Rule-0ing how it works, I have to assume that the core rulebooks are correct -- which means that your idea of the spell being cast (at all) is wrong.
I argued back that metamagic feats can also only be used on spells actually cast.
Ummm, but if you prepare a spell (for casters who prepare spells), then you use the metamagic feat that you apply to it. So how can you say that metamagic feats can only be used on spells actually cast?
... But, in an effort not bring the argument over here, I'm not going to respond to every point of your post -- just the above two, as those are the ones I need to have the most clarification on ^_^