Tasmania, and Victoria where we now live, are in the southern part of Australia ... the cooler part. Things like spiders etc., don't seem to grow as large in the cooler part of the country, probably because they don't need the extra body surface to keep cool.

If you were to travel further north, that's where you might notice the larger spiders.

BTW - I think what Rowan means by choosing grassy areas to camp is grassy, like mowed lawns rather than tall grass. If you're planning to camp in campgrounds, many have a grassy area (short cut lawn) for tents.