Whilst PG, Jessica, RTM, Trevor, Harj, Kirsty, Paul, Geoff etc and the other members of the team at Y Combinator are there to help founders, the most important thing that YC have created is their alumni network (YC have invested in 400 companies and ~1500 founders).

The network of YC also appear to be willing to pay it forward (in other words they are often each others first customers/users and they mentor, support and fund each other to success).

So to answer your question, can another Dropbox or AirBnB come out of YC with everything that the original Dropbox got? I believe the answer is Yes.