Sorry.. cliche alert!
You have a 10+ year old car and it seems far
more likely that some "specialist"
serviced the car at some time and then didn't re-fit the fan cover (or properly)... rather than someone in the factory
didn't fit the cover "just because it's going to Australia".
On the production line they don't know where the car is headed. It's easier to fit the cover to every car than try to tell the assembler (whose job is specifically to fit that cover as each car goes by) which one needs a cover and which one doesn't.
The scuttle cover isn't supposed to "seal" against the windcreen (i.e. water will
run past it, where it contacts the glass). It's job is to keep larger debris (twigs, leaves etc.) out of the scuttle panel.
Your mechanic is supposed to remove it and clean out the drainage channels occasionally.. but if they aren't capable of even re-fitting a cover, then expecting them to sweep out the dirt and mud that accumulates in the channels might be a tad optimistic.
Take it to someone who can do the job properly, or do it yourself..