the easiest way for me to explain it is this, the fuel lines from the tank all the way up to the rail, and including the rail hold quite a bit of fuel. alot more than you would really think. the reason (normaly) there is pressure right away is because the check valve in the fuel unit doesnt allowthe fuel to return to the tank afte shutting of...pressure remains long after the key is off...usually days. now, when the valve or an injector goes bad, the fuel cannot remain pressurized for that "immediate start" because the fuel has either leaked out of the lines all the way back to the tank, or it has leaked into a cylinder. therefore it has to fill those fuel lines all over again with pressureized fuel. if an injector is in fact culpret, a flooded cylinder will also account for the long crank time as it has to blow all the fuel from the cylinder and fire a foul plug.
i guess what i'm really getting at is the pump doesnt supply enough volume to fill the entire fuel system with fuel and pressurize it in the short amount of time as one would expect. it takes a longer time than usual. also the intial "key on" fuel pump cycle is alot shorter than a "bump start" fuel pump cycle.