Some things, like the computer language C, turing machines, lambda calculus, etc. seem to be "naturally" Turing-Complete. That is, they're just Turing-Complete from the bottom up.

On the other hand, cellular automata, many relatively simple Newtonian physics simulations and even [Legoes](http://www.youtube.com/watch?v=cYw2ewoO6c4), are also Turing Complete. This seems, somehow, just wrong, yet reductions are so common in TCS, how can we fault the reduction of Lego-brand blocks (and motor) to a Turing Machine by literally building a Turing Machine?

Is there any non-arbitrary way to say when the reduction required of a system is just too weird to consider it "non-ridiculously-Turing-Complete"?