The new AppleTV must have some form of flash storage, after all, it gives you 3 days to watch HD Movies, so the data has got to live somewhere. I wouldn't expect Apple's shiny new data centre to be able to serve all that content via streaming! (imagine the bandwidth needed for entirely on demand HD streaming...) Plus the device would have to buffer incase of network interruptions, so I'm guessing 4-8gb of 'invisible' storage maybe?
Anyway, we'll see when iFixit get their (exceptionally skilled) hands on one and reduce it to it's base elements...
Just like to say, I am so glad I was right! I can't wait to see where this goes!