These have been around for some years - (Devonport Tce Propsect has had them for at least 10 years!)
I am not sure what the specific requirements are re the placement of the cats eye, in relation to the hydrant, but from what I have seen, the eyes are not strictly beside the hydrant......
As for not seeing them in Country areas - many of the country towns either don't have mains water, don't have hydrants, or they water system is a private system, and the private operators (or in some cases cooperatives) haven't added the eyes.
On bitumen roads, it is certainly easier to find a cats eye in the middle of the road, than it is to try and locate the post tucked away under the nearby trees, on dark roads at night (which is what my brigade training was on Monday!)
Pip