The moment you boot into Windows 8, you're sent to a screen that looks and works very much like Windows Phone 7. It has the same interface in which constantly changing information is displayed on tiles that represent different apps, such as stocks, weather, and so on. The familiar desktop is just another app on the screen, and not a visually appealing one, either.
That means that when Windows 8 hits, millions of people will be introduced to the Windows Phone 7 interface, simply by using Windows 8. That's important, because the Windows Phone 7 interface is very different from the app-centric interfaces of the iPhone and iOS. Making people comfortable with the interface makes it more likely they'll buy a Windows Phone 7 device when they compare it to an Android one or an iPhone.
A recent survey from Connected Intelligence says that one of the main problems Windows Phone 7 faces is that people simply don't know enough about it. It found that of consumers planning to buy a smartphone, but not a Windows Phone 7 one, the main reason they're not interested in Windows Phone 7 is that they don't know enough about it --- 46 percent of them.
If they were using Windows 8, that reason would go away, because the interface they would see on a Windows Phone 7 phone would be the same they were using for Windows 8.
Beyond that, Microsoft plans to bring the cloud to consumers in Windows 8, and you can be sure that the interface and experience will be the same in Windows Phone as it is on desktop Windows, and as it is on Windows tablets. That will be one more reason for people to buy Windows Phone 7 devices.
Windows 8 won't be released for quite some time, so this isn't a quick fix. But Microsoft will certainly continue backing Windows Phone 7 until the release of Windows 8 and beyond, and that's the point at which the operating system might take off.