Exactly my point. The chip isn't designed to provide 2 simultaneous and independent image outputs; it's an either/or thing.
Um, no, wait a sec. A video camera exposes the sensor and simultaneously reads the result at 60 times per second (50 for PAL). In addition, if it has a variable shutter, it exposes the sensor for as little as 1 mS (1/1000 S) or even shorter. Every frame has to be read in 1/60 second, converted to digital, DV compressed and serialised for recording to tape. Then 1/50 sec later, it does it again. It's not a problem, this is well known technology. There are plenty of A/D converters that work in the MHz range and even at GHz rates for test equipment. Expensive, of course.
Granted, a still camera with an 8Mp sensor has a lot more photo sites than a video camera (Even the latest Sony HDV camera = 1920x1080 = ~2Mp).
It's simply a matter of designing the A/D converter to work faster. That takes more power of course, and still camera batteries are a lot smaller and last longer than a video camera battery.
I think it's simply a matter of power consumption vs battery duration (and price, of course).