in Australia from next year, new houses can only have gas, solar or heat pump hot water systems.

Which is, quite frankly, a bit ridiculous. Your house doesn't care a whit from whence the electrons came, only that they are there. An alternative would be to connect electric hot water to a certain tarrif, and reqire that the electrons supplying that tarrif come from renewable sources.

Further, from 2012 replacements of existing systems will also have these requirements.

So, if your EHW goes pop, you then have to shell out for an entirely new system?!

So, if your EHW goes pop, you then have to shell out for an entirely new system?!

Most failures of hot water system is the tank developing a leak which means replacement. However, if an element or a thermostat fails then I am sure you would be able to get replacements.
The replacement costs may not be so bad - currently in Sydney companies are advertising solar HWS for $350 after rebates which is cheaper than a conventional HWS!

Lets think systematically.
Evey solar hot water system installed (electric hot water booster or no) also reduces the strength of the baseload power arguemnt.

Those cheap tariffs are there for a reason.
We heat our hot water using electicity at night why?

Not because we have no choice.