I think the reason that both numbers (elapsed time/ endurance) were the same, is because the elapsed time on the route was expected to be 4:22. There's not really much you can do to 'sharp pencil' that.
The aircraft on the other hand, would have had a number for endurance (don't forget, this a/c was full of fuel and nearly maxxed out pax wise, so real heavy) of less than 4:22
So they increased the 'endurance' number so as it would not be less than the 'elapsed' number.
I don't remember too much about the RJ limitations now, but can you fill it right up with fuel and then add 81 bods?
Must have been mighty near MTOW