Nope, it’s not going to be required for a device to have a gyroscope.
Brandon Watson, speaking on Channel9 says it’s a great idea but it’s not
there at launch and an accelerometer is very robust.
So, Windows Phone 7 won't have gyroscope at launch and the API for the accelerometer won't be ready. I presume it's official information, since Brandon Watson (Microsoft's Director of Developer
Experience) announced it.
He also said that pivot and panoramic controls in the developer tools will come out by the
end of the summer.
The full story can be found here.