I had a problem with Holden about three years ago when they wanted to charge me $1400 to have my brakes fixed and it turned out there was absolutely nothing wrong with my brakes. Now they're telling me that the fuel-injection system on my 2007 Astra needs cleaning, even though it's only done 23,000 km. How many kays do you need to do before you have your fuel-injection system cleaned?
There is no set distance and it is usually only done when the engine starts to run a little roughly or loses power. It sounds to me like your dealer is trying to sell you up to something you don't really need.