Your assumption is also WRONG.

Pins wake up from RESET with the output port latch bits set to 1's. This makes the 8051 driver be let go from the port pin and lets the weak pullup establish a high level on the pin. In other words out of reset the pin is set so that it is capable of being used for input OR in the equivalent output high state.

If the pin is intended for output after reset and you want the output at a "1" you actually have to do nothing. The pin is high already. Only if you want the pin to go low to a zero would you then write a 0 to the port latch output bit. This engages the 8051 port driver to pull the pin low. The 8051 port pin driver never itself can pull a pin high....it is always the weak pullup that pulls it high...OR an exteral additional pullup resistor OR an external circuit hooked to the pin that sources current and makes the pin high.

Period !!
Michael Karas