Yes it is a bit of a rort.
OTOH it does mean I get lots of call outs for "black smoke coming out of my mower and it is running very slow".
So I show them how to clean out the pre filter, book in a servoce for latter on and don't charge a call out so get a life long customer who thinks I am great even more so when he finds out the place he bought it from charged some one else $ 90 to come out & do the same thing.
It is staggering.
I do annual services on B & S engines and they are just about choked closed.
Honda's are even worse. Some have so much crud in there you have to pry the filter out .
I have never had to replace a Victa ( or Rover or Super Swift or Greenfields ) air filter because it was dirty, ever.
Usually they get so many spider webs in there , red backs primarily , that the dirt & grass stuck in the web is all that needs to be removed.
Done some mowers 30 years old still with perfect original air filters.
They do get replaced as part of a 10 year service along with the 5 "O" rings ,fuel lines & cut out boot.
That will keep the power torque running well for another 10 years.
Here is what we used o get down here
The filter sits in the cylinder up the top