The thing to remember about Apple and Macs is for Apple sales a large percentage of sales is actually to schools upgrading from older Apple systems. Pro photograhers will often see a Mac. But when looking at what people(average consumer) are buying off shelves in retail stores(Dell, HP, Sony, Toshiba, etc. desktops, laptops) what is on those? Windows!
Take a look at any laptop stocked at Best Buy, Target, CompUSA, even a local Walmart and what do you see there? Windows again! Don't expect to see all units with 7 preinstalled there however! Vista will still be the dominent OS on machines they are still trying to move out of their inventories. It will still take some time before all you see is 7 machines stocked.