Hi Brian, Your point is true for the conditions you set (using the whole frame). But using a prime lens to shoot sports means that most photos will have to be cropped. To provide the greatest latitude for cropping and still allowing a large high quality print, you want the best resolution that can be obtained from the equipment you have. This is my point – I can’t think about what is the minimum number of resolved pixels I need but rather I think about how many I can get from the equipment I have. The optimal shutter speed to limit motion blur then becomes pixel density dependent (along with several other factors including focal distance and the subject’s transverse speed). And for my shooting conditions, I find that 1/800s is better and 1/1000s is best when I have enough light.
A completely different mindset is to shoot for a purpose such as the web or maybe a small or medium sized print. At that point, I agree that if you optimize for minimal motion blur at the pixel level then you might be optimizing the wrong variable because most recent DSLR cameras have plenty of pixels to "burn".
Sometimes I do drop to 1/500s when the lighting simply demands it – and in these circumstances I know I simply can’t get high enough quality for a large print due to noise and/or motion blur. Sometimes I’ll bring strobes … but that’s a different story and I have not done that for awhile (here’s a basketball shot with my old D70 using multiple strobes at 1/500s.) I really miss the 1/500s sync speeds.