I have a mostly-105 road bike (triple) with 105-5603 shifters/FD/crankset and an ultegra-6600 RD.

I got Ultegra 6603 shifters for christmas, and was going to install them and move the 105's to my commuting bike (which I'm installing a touring triple on). I was just about to make the switch on the road bike, when I stumbled upon this on the shimano website:

http://bike.shimano.com/publish/cont...ty%20Chart.pdf

Why does it list the 105-5600 separately from ultegra/DA for front shifting compatibility? I thought all front shimano road shifters used the same pull ratio, that separation I haven't ever heard of. Is this just a marketing thing, or is there some credence to this?