Centaurus
The point you make is a good one, although on the kind of runways used by most UK light aviation, it is almost academic. Accelerate stop in my light twin (that is: closing the throttles at Vr and applying maximum effort braking) uses up about 1100 metres at MTOW. On most runways therefore once you've unstuck, you are not likely to land on succesfully and should retract the gear ASAP.
In a light single (to return to the original question), accelerate stop distance is likely to be significantly less and the idea of retracting the gear only once insufficient runway exists becomes more relevant. On a short field though, you are in the same position as a twin, in that you are not likely to be able to get down on the runway remaining once you've lifted off, so getting the gear up becomes a priority.
-2Donkeys