I asked the Bike Hermit about this. Here is his reply:

For a 700x 32 tire, the second number is the nominal width in millimeters of the inflated tire. In practice a 32 width can be anywhere from 28mm to 33mm or so. Tubes are balloons and are sized to fit a range of widths...just get tubes that include the width of your tire within the range. The other number (32mm PRESTA) is the length of the valve stem.
The Surly website means tires up to 45mm wide will fit, but if you want to use fenders too, go with a narrower tire because the fenders need to be wider than the tire. I use 700x 35 Panaracer Pasela tires and 700x 45 Zefal fenders on my Cross Check. In your example the 700 x 45 fenders will be the best choice. I know that fenders up to 50mm wide will fit on these bikes. More on fenders at Bike Touring News