Appealing to an audience

I'm wondering- do authors write with a specific audience in mind? If they do, does that cut other audiences out?

The reason I'm asking is that I am still reading DIRTY WEEKEND by Gabrielle Lord (how having to work cuts your reading time down!)
Lord is writing in a male persona, using Australian colloquialisms quite liberally. (Where else would you find up at sparrow fart but in an Australian novel?) I'm trying to decide whether she tries really hard to bring out the Australianness of language and setting, or does it just happen?

Last year oz_mystery_readers discussed DEAD SET by Kel Robertson, coincidentally also set in Canberra.
Here is what I recorded:
The Hon. Tracey Dale, Australia's Minister for Immigration (ALP) has been murdered in her Canberra apartment. She was the author of Australia's current immigration policy: the Compassionate Australia Program, which has recently resulted in significant increase in Australia's refugee intake. Some believe her death is the work of terrorists, or at the very least racists. Federal Australian Police Detective Inspector Brad Chen is returning from sick leave of 3 months, and this is his first case back. Some would see him as a man with many handicaps: still on crutches after being knocked down by a car, an Australian-Chinese with Chinese appearance but unmistakeable Australian accent, addicted to pain killers of the worst sort, and named after a cricketer. DEAD SET is almost a political thriller as much as a murder mystery. Set in Canberra and Melbourne. As Chen's investigation proceeds, the list of suspects grows, and others die. Tracey Dale ignored a time bomb, something that spelled political ruin for her. A debut novel for Kel Robertson.
I ended up wondering what non-Australian readers would make of the language and the local political references. My rating was 4.0

Some non-Australian readers tell us they need a glossary of terms to help them read an Australian novel. And yet I don't think that happens when they read Adrian Hyland's DIAMON DOVE.

So what do you think? Does writing for a specific audience mean the novel will have limited appeal to readers who don't identify with that audience?