Ace, I think you're right, someone did mention something about using alot of resources to animate weather.
I'm not an expert at Flash programming. It appears though a rain effect in Flash could use a lot of CPU resources. Much like the moving dots on WGT's greens. That's why we all turn off the dots when we're using the meter!
This little rain animation , when being viewed, uses an additional 10 to 15% of my CPU resources in the flash plug-in. I'd expect a similar increase in the WGT game if rain were added. Then add some more CPU usage for tree animation due to wind. I think we'd all be turning off the weather for a smoother meter.
But who knows, think of the avatars with rain gear WGT could sell!