Interesting question. The conditions attached to the subclass 482 visa state that:
holders must [...]
commence work within 90 days of arrival in Australia, if the visa was granted while the holder was outside Australia
This is probably intended to say that your visa will be cancelled if you don't start work within 3 months. However, in your particular situation, it sounds like it's also OK for you to visit Australia without working for up to three months!
That said, I would not enjoy attempting to explain this to the immigration official on arrival, since if they find out you don't intend to work in the job you got the visa for, they will quite reasonably wonder if you're planning to work somewhere else illegally then. But then again, given that you already have a firm US job offer (and visa, I hope?), it should be possible to convince them that you will not.
Long story short, if you want to play it safe, it would be wise to get a regular Australian tourist visa. But if you're feeling lucky and want to try your current visa, you appear to have the law on your side.