The sales guy hit the nail on the head. I can lock up my linear pulls on my Devinci, just as easy as the disks on my Trek. L-pulls, I feel, are better for commuter bikes for the following reasons. Lighter, super cheap to maintain, and better suited to road riding. As for raw braking performance between my three bikes.
1-Hydraulic disks (MTB) 27 lbs
2-L-pulls (commuter) 21 lbs
3-Side-pull (carbon road bike) 17 lbs
It is funny, the lighter they get, the worse the performance. That being said, all three bikes stop on a dime. I would never thrash through the bush with side-pulls or L-pulls. Disks are awesome at isolating themselves from mud and A LOT of water. Plus they do modulate better. But I have never found myself a road situation, where I felt I needed them, dry or wet. In theory, in dry conditions, rim brakes will fade a lot less, as they have way more surface area to work with to dissipate heat as well.
I would highly suggest, if going the Devinci route, look at the one I suggested earlier of the 2 in the fitness commuter category. This years Oslo is a MTB/road mix, and the model I bought last year, would be considered a fitness this year. Plus the tires you want are 700x28 for commuting, I actually went down to a 700X25 (which is as narrow as you would want a commuter tire). The 2012 Olso is a 700X32. Plus the wheels on that top model (melbourne), are worth the price upgrade alone. Wheels/tires are your # 1 priority in achieving speed. The narrower and lighter the better. Lastly, it looks like the Melbourne has the Kenda tires that came stock with mine with the reflector strip. If you are a TRON fan, you'll dig'em. This is how people will see you at night, and this was just my iPhone flash, not a set of HID's lol:
