Here is a pic of my truck with the closed spoke wheels and 30" tires before I put on the 15x8 open spoke wheels:

 

Yes you are correct. My generation Dak comes with 15x8's, but mine did not. It was spec ordered with the 16x8's and has NO suspension or body lifts on it, so the 16x8 will fit stalk even up to a 265/70 series tire stalk.

 

why wont The open spoke late model rims (15x8) fit on a 2wd?

 

the 2wd doesn't have as tall a stance as the 4x4, and the front suspension is obviously different for the 4x4. Biggest problem I've seen is the front tires come into contact with the airdam on turns and sometimes on bumps, some people take off the airdam or cut it to take create clearance (looks like crap without airdam on a 2wd), I've seen it done on one 2wd, but the truck sold before I could get a close look at it, he DID have 31" tires on it which caught my attention, looked like he stripped a 2nd gen of it's tires and rims. They did stick outside the fender flares 1/2 an inch so I'm guessing he used spacers on them, they also came really close to the airdam, didn't look like he adjusted it either.

 

My 02 had 16" steel wheels whith chrome covers, I swapped them out for the 15x8's.

Tire size calc - 265 mm (25.4 mm/inch) = 10.4" wide, multiply by 2 (two sidewalls) and again by .75, or .7, or whatever (265/75r15) for the aspect ratio, and add the wheel size 15 to get the height. Or use a website calculator.

The 31x10.5x 16 converts to roughly 265/70r16 which was the stock tire size that was on mine.

16" tires don't come in the standard size, only metric.