Well folks, it's not just B&S' agenda at work here.
What's behind this, from the regulations point of view, is a Federal Government plan, under the umbrella of the 'National Clean Air Agreement'.
As CyberJack has said, at present there are no emissions rules at all for 'small engines' in Australia [unlike many other countries].
But that is planned to change in 2017, and will effectively spell finis for the 2-stroke mower engine here. This has been in the pipeline for a fair while now.
The applicable Work Plan is
HERE - 100kB PDF.
THIS Outdoor Power Equipment Association Aust doco has a more detailed rundown on what to expect.
The 2010 Regulation Impact Statement, and many of the industry submissions made on it, are available
HERE .
While the technology exists to build a compliant 2-stroke mower engine, I don't believe it would be price-competitive with existing 4-strokes. Unlike say outboard boat engines. Particularly now that mowers have essentially become a 'disposable' item, rather than a 'repairable durable' good.
By the way, these rules will not apply to existing engines, just to new ones offered for sale.