A very good question posed by Bar Shaker. I don't have any figures to hand, I'm afraid, but leaving the issue of parallel runways aside, each runway and departure has a protected area which is guaranteed to be clear of obstacles. This protected area provides a straight margin of safety, either side of the runway, and then expands in a cone from the departure threshold.
Assuming a runway of (say) 1,850 feet, and that a light aircraft or microlight - while using the full length, may rotate within the first 300 ft or so - at which point would you deviate from the centreline? Any immediate deviation, would surely take you outside the protected area into potential conflict with obstacles, such as the tower, masts, antennae or other buildings.
A deviation past the threshold would be less severe, providing it remained within that expanding cone, (which I can't remember the figures for). However, I doubt it is a significant enough angle to make a lot of difference as you describe.
However, the mantra of "no turns below 500 ft agl" it has to be said is going to be a "catch all" phrase which would work at any airfield. Indeed, on a long runway, 500 ft may well be achieved within the airfield boundary!
So as Genghis the Engineer pointed out, it's all down to local procedures and knowing the airfield.
I would point out, though, that there is no rule to say that you need to "make the runway" if you did elect on turning back. Landing across the runway, or on the grass, or on an alternative runway, or even on a taxiway, the ramp or the carpark, are all viable possibilities. The only logic to the decision to turn back is if there are no viable landing spaces available ahead. The other advantage is that the emergency services based on the field can get to you a lot quicker.
Other than that, I would encourage any pilot to know before takeoff what his / her options are. At Titusville, in Florida, one runway would drop you straight into the river between the field and the space centre. You really should know that before you take off and be prepared for a possible ditching.