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Sounds like you've only seen it done properly! I can assure you a simple concrete base is a luxury option in the back gardens of SW London. Hauling a whacker into the garden down the stairs puts people off using them.
Airhead-
I've only ever done it properly.
First one I did was part of a renovation in Earlsfield. We did it properly including lugging the whackerplate through the house.
It very nearly went horribly wrong because the labourer thought he could make it easier on his back by turning the whacker plate on and driving it through the house over the freshly laid French oak herringbone parquet. Fortunately he couldn't get it started in the time it took us to realise what was going on and (obviously doing so in a very respectful way) explain to him that a couple of bits of correx wouldnt offer that much protection.
Bobbo
I've never heard of putting AstroTurf onto a concrete base.
It's normally type 1 sub base whacker plated down until level, then grano dust on top that gets brushed then whacked and swept then whacked again until it's billiard table smooth.