posedge clk vs posedge clk, posedge reset
The sensitivity list determines what is clocked and what is not. If the signal is in the sensitivity list, it can make a change to the signal without being on the clock edge, so in the syncronus case, if the reset is asserted, it won't happen until the clock edge.
In the async case, it doesn't matter what the clock is doing, the reset signal will happen right then.