There are many differences of bitcoin and real money.. bitcoin you can use it online as alternative real money you can buy anytime there.. in bitcoins you should have too because many other will exchange it fast and instanly in our place.
You have point and well they are both currencies used for different transactions as well as being purchased for our necessities. Bitcoin is different from real money in the sense that it is volatile and it may deflate and the money that you have may be less than the other day, but it may pump soon thats the reason why investors come here they can be profitable here, and paper money was the local currency we used for small tramsactions.