When the Apple TV first launched, you were limited to 200MB of an initial download and 20GB total counting later-downloaded on-demand resources. These on-demand resources in theory automatically get flushed out, so the HD space serves more like a cache. So the 32/64GB has a very tenuous relationship with performance before, and now that it's been raised to 4GB install probably will not be nearly enough space. It's a weird device.