Microsoft has been reaching out to various sites to shed some light on the situation.
In reality, SP1 will not be required:"Internet Explorer 9 will work on Windows 7 RTW and Windows 7 SP1. When you install Internet Explorer 9 on a system that has Windows 7 RTM installed, additional operating system components are included as part of the installation of Internet Explorer 9. Those 'additional operating system components' will be part of Windows 7 SP1. Either way, this will be a seamless process for the user. Just wanted to make sure you had the latest."