thanks for the explanations, I think this helped a bit (still need to sleep to let everything sink in).

A key for me is that XRP is not like the other currencies. They are a real "commodity", like bitcoin.

Are there XRP IOUs at all?

One question the answer to which might shed more light into my mind: Say by brother and I both use ripple and after a while we determine he owes me 10 EUR (or he owes "the world" 10 EUR and "the world" owes me 10 EUR). Would it be possible for him to give me a 10 EUR bill in meatspace and somehow reflect this "settlement" into the ripple system?