Top of the mornin' to you Gary! Interesting, isn't it? Top-nailed or secret nailed... T&G just creaks regardless... I guess because of expansion and contraction and the pressure with with the boards are stacked by floor cramps or the secret nailer.
It's reminiscent of the trees from whence the timber came... if you've ever climbed up and spent any length of time up a tree in a gentle breeze, the things are just making noise the whole time.. branches creaking against each other, leaves hitting each other (each leaf hitting another leaf is a barely audible thing, but put them all together in a strong breeze and they roar like the surf!)
That's the beauty of working with a living, organic material like timber.. it just has infinite complexity and beauty which no other material can match.
On the subject of subfloors, Australian builders have been using particleboard subfloors for about 15 or 20 years (there are examples earlier than this, but typically they weren't the modern water-resistant variety and so were quite unpopular.) Generally these get covered with carpet. It's somewhat rarer to see timber on top of a subfloor here unless it's parquetry, simply because of the cost - it's cheaper to nail the strip flooring directly to the joists rather than to lay a subfloor and then put the final floor on top of that. Cost and time are huge considerations where one could be paying between AU$3 and AU$5 a lineal metre for the timber floor. It all adds up and the mindset here is that we are still living in a frontier country, with minimal resources (1 person per square kilometre, driest inhabited continent on Earth, old-growth forests in real danger of being totally clear-felled etc) so there is a philosophical push to ensure that everything is used sparingly.
Our industry has woken up to plantation timber over the last 20-25 years also, and we are starting to see the first crop or two of popular native timbers like Hoop Pine and Spotted Gum coming out of these farms. Spotted Gum, in particular, is a very interesting timber. It is incredibly hard and resilient (it is often used for making axe and sledge hammer handles because it's so unbreakable) - but it is also somewhat waxy and fine-grained, so smooth-cut boards will slide easily over the top of each other. It can vary a lot in colour and grain patterns, making it visually stimulating and quite beautiful - and now that it is coming out of plantations, it's price is getting better.
Some of the timbers we have here are so hard that they will not take a pneumatic nail at all - and six-inch steel manually-driven nail needs to be pre-drilled or else it will not drive. Some years ago, my father and I worked on a house with studs and top/bottom plates cut from such timber. The first day I started nailing together some of these boards with a 75mm pneumatic framing gun, and the nails just either bounced straight out or bent like plasticene. My father gently took the gun out of my hand and handed me a drill and bunch of 6" nails..
it was as hard as steel and we were forced to sweat it out in the hot sun, manually hammering together this frame... if you get flooring joists made out of that sort of timber, then you have to manually pre-drill and nail each board because no flooring nailer or stapler on the market today will be able to drive a nail into it. Even the Porter-cable secret nailer we used a couple of weeks ago had trouble in some of the joists and we had to manually punch the cleats in.
All the best,