I've been wondering about this as well. Why are they using so few images? To me that is like reverse blinking: Instead of keeping your eyes open, and blinking for a short amount of time every now and then, you're walking around with your eyes closed, and open them only for a short time.

I believe the main problem is knowing which data to trust and which data to discard. Reflections (water, shiny surfaces), moving objects (leaves in the wind), over-exposure, and lens flares are already pretty hard to deal with. But with low resolution data, you make it even more difficult because there's more data to discard for being too inaccurate.