Any reason not to use strong flour (also called "bread" flour) in this recipe? Why would a recipe for bread call for all-purpose flour?

I've made this once with AP and once with bread flour adding the extra liquid. Maybe it's my imagination, but I think the AP version had a better texture. There wasn't a huge difference, but there was a difference. The original authors specified AP with the added advice regarding using bread flour. In baking, I almost always go with the authors directions. If you have bread flour that you need to use, go for it. If you have both, I'd go with AP.

To answer the second question first, all-purpose flour results in bread with a somewhat more tender crumb and less chew than bread flour, which is higher in protein.

You could certainly substitute bread flour in this recipe, but if you do you should increase the water slightly (5 to 10 percent), since bread flour absorbs more water than AP flour.

I'm guessing their original recipe was written using all-purpose flour since it's the flour most people would tend to have on hand and their objective is to make it as easy as possible for people to make bread every day. They do note how to change liquid levels if you'd like to use bread flour here:

http://www.artisanbreadinfive.com/2008/02/10/qa-flour-and-water

You also might try asking them on their website, as one of the co-authors suggests in a comment on the recipe:

"Hey all:

I'm Jeff Hertzberg, one of the co-authors of The New Artisan Bread in Five Minutes a Day, where this recipe comes from. If you have questions about the recipes, just post one on our site: BreadIn5.com -- at any "Comments" or "Reply" field.

And yes, the 5 minutes refers to the active time required for each 1-pound loaf.

Jeff"