I would argue that LEGO hides them just as well if not better than Apple.
The "not too loose, not too tight" thing is part of it, but isn't actually the key reason which is "accumulation of tolerance". Imagine two rows of 100 bricks. The difference in length between the two rows is 100 times that 1um tolerance. If the tolerance was less good, things wouldn't fit together well.
Lego model design guidelines actually have a maximum size of a "fully" connected block of bricks because eventually even this precise manufacturing can't cope. Really big models have purposefully designed decoupling between sections.
Doesn't tolerance work both ways? One brick is 1um longer than it should, another one is 1um shorter - in the row of 100 bricks those differences will mostly cancel each other out, won't they?
Also, it's not just about variance between different bricks (1x1 vs 2x1) it's about variance between different parts out of the same tool (the correct term for a mould is a "tool"), and variance between different tools producing the same brick.
Some really subtle effects affect the size of parts if you care down to the level of 1um - all sorts of temperature variation, pressure, humidity, colour mix etc.. Lego's skill is the ability to control or compensate for all of these confounding factors and get consistent results, regardless of age of mould tool, manufacturer of machine, ambient conditions etc.