LineChaser, looking at the statistics for laptopgpsworld.com, last month (July 2010), people found this website though 41,290 different keyphrases used on search engines.
"streets and trips for mac" was the #41 most popular search term for the month. So I think there is some interest for Streets & Trips in the Mac user community. But that may not be enough for Microsoft to go that route.
It would be cool to see Larry & Gladwin attend Macworld, and other Mac shows, promoting a Mac version of Microsoft Streets & Trips.