True but will you be able to take a 1/10th handheld shot of something stationary in an extremely dim situation at 70mm like you could with the 24-105L?
Both have their merits but I still stand by better IS than no IS. How often are you gonna shoot action in low light situations?
Low light shots at slow shutter speed begs for a tripod -- IS or no IS. I can always control control camera movement with a tripod/monopod if needed. How are you going to stop motion with IS? I often shoot moving objects in low-light/indoors. Even though you ask people to hold still they still move a bit, and that goes double for kids.
Give me a fast lens over IS all day, every day. Not to mention the better subject isolation with the narrower DOF and better bokeh.