That'd only be worth doing if the cost of hiring a replacement and getting them up to speed is less than just paying 2 months' salary. Sometimes true, sometimes not true.
Beyond that it varies by state. In New South Wales, from what I can gather, the employee can cash out a pro-rata portion of the benefit upon termination if they've been employed for longer than 5 years, unless fired for misconduct. So you'd have to lay everyone off after 4 years 11 months to keep from paying out, which would increase the cost of employee churn even more.
Strange as it may seem, some emplyers value their employees and replacing someone after ten years is going to be a hell of a lot more expensive (in terms of lost value an retraining) than 8 weeks paid leave.
Besides which, you'd probably get screwed in an employment tribunal (IIRC Australia doesn't have 'at-will' style employment like the US)
That is absolutely what would happen here in the U.S. if we had such a law.