Sandor,

you are a funny guy! I think you will find the explaination in the bible.

All instructions listed in your posting are read-modify-write instructions. The instructions read the latch, not the pins, possibly change it and then rewrite it to the latch.
The reason for reading the latch instead of pins is to avoid misinterpretation of voltage level at pins. Why?
Because there are certain situations, where 1s was written to latch, means pin is in high state, but voltage at pin is not high enough to deliver logical high state when being read back. Assume for instance, that you connect the basis of a transistor directly to pin, while connecting emitter to ground. Then, when latch contains 1s, according pin will show high level, means internal active pull-up is turned-on delivering some current to turn-on this transistor. BUT, keep in mind, that basis now is only about 0.7V above ground level. So, when reading back only pin voltage, instruction will not realize high state at this pin any longer, but misinterpret base voltage of 0.7V possibly as low state!! That's why the latch is read back and not the pins.

Kai