If you knew anything about how exchanges work John, you'd know that withdrawal limits are typically imposed by the banks themselves and/or AML rules. Not your entirely unfounded theories about them being fractional reserve. Mt Gox has made many references over the years to having to negotiate with banks to up the amount of money they're allowed to transfer per day. Just one more reason why the banking system sucks. There are typically no withdraw limits on the Bitcoin side once AML verification and good security are set up.