The point of earthing devices is that if (realistically when) there is a short to a part you can touch a circuit is made, current flows rapidly for a very short period of time, and then the over-current protection on the branch trips alerting an onlooker that there is a problem. Neutral is tied to ground to that the potential danger of a short can be sensed and protected against.I think a better example of the importance is a toaster that is shorting mains to it's chassis. If it's grounded the circuit breaker pops every time you plug in the toaster and you either fix it or get a new one. If the toaster isn't grounded mains potential is sitting there at the chassis of the toaster waiting for you to complete the circuit to earth (like touching the toaster with one hand and sink with the other). The second situation leaves you in significant danger. If the outlet is not protected with a GFCI you might see several amps flow through you for several ms before a traditional magnetic breaker trips. This is more than enough to do serious damage and/or kill depending on the path. If neutral is not tied to ground then there is no certainty that a short will trip the over-current protection.
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