When the intake valve is closed, there's no flow through it. When it opens, there is.
Not too sure why you're stating the obvious here..
When the valve closes, you have the momentum of the air still in it heading towards the valve. It then bounces, more or less, off the closed valve, creating the pressure wave that spencer was talking about.
Also, a misti engine tends to rev higher than a big fat 8, making its usable power up higher, and therefor has a higher intake velocity.
Big v8s are usually geared a lot lower, so their engine revs at the same vehicle speed is lower, meaning lower intake velocity.
On top of that you haven't taken into account the specific design of the ports, valves, or anything else at all.