I think it's the way the character moves. If it doesn't feel natural to the brain then your going to have problems. In rigs your playing a seated character inside a moving machine. The brain expects this and can handle it.This is what I think too, but that's not inherent to Minecraft. They just need to fix it.
I'm not really sure that's the case. Look at t=60, it's very up front and personal. Maybe it is the case.