You're average purse/murse is about 4-6L, and that won't significantly slow anybody down or block the aisle. The 40-50L rolling luggage, the large travel totes (30L?), the 30-40L backpacks all take some manuvering to get down the aisle in a hurry. Those do slow people down.

The safety requirements for a passenger jet are evacuate everybody in less then 90 seconds from a full plane. The crew accounts note that it took several minutes to evacuate the half empty plane with only one emergency exit out of commision. This speaks very poorly of the passenger body.

Had the fire not been noticed until after the point of no return (the point at which the aircraft does not have enough runway to abort the takeoff), the pilot's only options were to either drive the 70+ ton plane off the end of the runway, and maybe across Paradise Rd or Las Vegas Blvd. Or, take off and circle around while on fire. The aircraft was already upto 90kts on it's take-off roll when the fire was noticed, and a few more seconds would have put it past that point. Either one would have resulted in a much smaller window to evacuate the plane where any delay could prove painfully fatal to the unlucky schmiels farther from the exit.