I think they play a similar role in Australian visual culture because both are often used as shorthand/symbols for "Australia". Think of a Qantas commercial, or a tourism campaign to attract people to Australia - neither could be complete without a shot of both of these things. They are generic symbols of the nation.
This tends to drain them of the more signficant meanings they have in other contexts, e.g. Sydney Opera House can also be seen as: (1) a 20th-century architectural marvel; (2) a symbol of "breaking the rules", as Utzon's design breached the competition criteria; or (3) a symbol of Australia's post-colonial desire to be taken seriously as a cultural power by devoting a prime site, loads of money, and magnificent public building to a niche artform enjoyed mostly by rich Europeans. Similarly, Ayres rock (aka Uluru) can also be seen as: (1) a unique geological phenomenon; (2) an element of indigenous stories and culture; (3) a symbol of white exploitation and abuse of indigenous tradition by allowing tourists to walk all over it.
Each can be given a different "semiotic" meaning (i.e. a value as a sign) depending on the context in which the image is presented, and the knowledge/experience of the person looking at the image.
