Why Does the And Gate have Two Transistors on Top?
If the upper two FETs weren't there, then when either A or B was low there'd be no path from the output to any driving potential. The output would be in the high-Z state rather than driving a high output. 

If the gate isn't meant to be an "open-drain" type, it needs to be able to have a low impedance output for either a low of a high output value.

On your edits

The BJT circuit will also work (this type is generally called resistor-transistor logic or RTL), however,


It will consume more power because the resistor will consume power whenever the output is low.
It will not be able to provide as much high output current before the output voltage sags below the minimum \$V_{OH}\$.
The low-to-high transition will be slower because any load capacitance will have to be charged through the resistor.
The low-to-high and high-to-low transitions will be asymmetric (not the same slopes), which can cause issues in some applications.
If implemented in an IC, it may be costlier because resistors generally require more die area than transistors.