peter pusset,
Those factors are related sometimes to the media you buy, battery life as well as the camera make model and design. Most everyone is aware of this who has used 4 or 5 digi cameras or so and it sucks. It's not groundbreaking news and it's not just your Canon.
The best solution to capturing an action shot with a digi camera is to hold the shutter button down to half way until the "right moment" then all the way for the shot.