The takeoff speed (V2) is dependant on field elevation, weight of aircraft, outside air tempture,, runway condiitions, (slush, rain, etc) and any obstacles that need to be cleared, normally the crew (should) consult the charts in the aircraft operations manual.
A couple of years ago I had to treval from Portland Oregon to Salt Lake last minute. (and back) I found that I could fly first class for less than coach if I booked at the last minute. It was a short flight - 1.5 hours - and no meal was served. So they probably did it to keep loyalty at no extra cost.