Yes indeedy.. But having said all this, there is nothing stopping you from flying down to Sydney (from about AUD$100 one way) if it's MTBing that you're wanting to do, you can stay over night in the lower blue mountains, hire some bikes (AUD$40/day) and go ride. heaps of good tracks in the lower blue mtns.
Otherwise, you can have the best of both worlds by staying in downtown Sydney say the Holiday Inn in Potts Point, get up really early and get a train (or drive) up to the mtns (glennbrook aprrox 90mins) do a few long rides. then head back into town to paint it red

the next day could be spent walking around town..
but you really need a min of 3 days Fri,Sat & Sun ie. Fly down late Friday, ride early Sat am, fly back late Sun. Quite hetic, but it'll be lots of fun. esp if you stay in Potts Point as it'll be close to where all the night life is.