Legos famously have a weirdly high tolerance for injected molded plastic*, it's part of the branding they use to justify their high price. It does make them snap together more reliably than Mega Blocks or whatever, but Mega Blocks or whatever usually snap together anyway, so I don't know whether that extra precision counts as necessary.
* People quote all sorts of tolerances for this, but the most credible-looking one I found was 0.04 mm.
