I suppose anything's possible but what would be the point of that design? Do you think Apple wants to prevent you from accessing your data too fast?
Of course they would if it makes me want to splurge $1300 on their overpriced SSD!
Anyway, I'm not necessarily saying this conspiracy theory that they're making it slow on purpose. Does Microsoft want their browser to be awful? Does Dell want to make crappier AIO's than Apple? Bad design doesn't mean they want to make it bad.
It's not a far out suggestion. It makes sense in a way, if I haven't opened a file in a few weeks it doesn't seem that unreasonable that Fusion might think of it as "unused data" and move it onto the HDD to give a bigger write buffer on the SSD. Does make perfect sense in a way when you think about it.