how much will price fall on ex dividend date?, page-23

Here is how I see it.
The dividend is worth 20c to most australian investors including the credit, but:
If you can't claim the credit it is only worth 14c. This could be some foreigners or pshort term traders that don't hold the stock 45 days and earn over $50000 in credits in a year.
If you are entitled to a consessional capital gain you may be better selling today and buying back at a later date. Dividends are taxed more than gains for most who hold over a year. But the gain size is obviously different to the dividend so that is a factor too.

So it normally falls between 14c and 20c and almost all investors can get a windfall if they know whether they are better off holding or not.