Hey Kev,
Turbo Otter presents a good reason. The somatagraphic illusion that is presented to pilots at night when climbing away into a dark area with no backlights can give the false impression to pilots that the aeroplane is climbing too much so a pilots natural response is to nose down slightly, but he/she does so without realising that by doing that, the plane is now flying straight and level or possibly in a descent, hence the reason why its vital to confirm a positive rate of climb.
The practice is followed over into the daytime primarily for the reason of confirmation of climb. Horizontal or vertical windshear can be a problem from nearby microbursts or thunderstorms hence its important to double check your climbing before raising the gear so you don't settle back onto runway on the aircraft's belly.
I normally confirm gear up at about 200' no matter what the runway length because by the time the gear has retracted, you would be at say 300' - 400'.
If you suffered at engine failure at this point then there would still be adequate time to lower the gear to land back on the runway or possibly some paddock/road ahead.......if its water or dense forest - then maybe best to not even lower the gear at all........
hope that helps.....
Mr G
