Yeah, they saturate, as do many other physical systems... We can't get a real 'population explosion' either... It will saturate. The problem is that 'saturation' for a population might look rather nasty, if undamped. Very ugly oscillations.

In electronics most people are not stupid enough to propose an unlimited growth model. Or rather, the basic model is, sure, for many things, like amplifiers... And it is very, very useful, this model. However, anyone who has ever built a circuit knows that it is indeed bounded, and the region of constant gain/growth is limited... The constant gain model is only useful for a range of inputs... Unfortunately most economists seems to disagree that their discipline, as it is based in the physical world, will have very similar bounds to the constant gain/growth model. They come off a bit like first year electrical engineering students. Confusing the model with the system, and failing to properly take into account how it is premised on limiting the input to a certain range...