Australia's energy regulator (http://www.aemo.com.au/) runs a separate pricing market (ancillary) for producers who are able to provide black start capability to the network, amongst other things like frequency regulation (I think...).
I can't speak for Australia, but I know that both are true for US pose markets. Power is a big part of what's sold, but there are many other markets too. Black start services, generation capacity, and frequency regulation, just to name a few.
Part of the key to serving electrical demand is having a balanced mix of generation to serve your load. Some units are better running flat out, some are better for brief periods at peak demand, and some are good at quickly taking up the slack if another unit fails. Different power markets exist within the same geographical footprint to ensure that all these types of needs (and more) are met. (24 hours a day, 7 days a week, and into the foreseeable future.)
