I believe that fresh milk is avoided in part because it is easier and more convenient to use dry milk powder but also because there may be food safety issues if fresh milk is not properly refrigerated. Also, Tom Lehmann says that one should scald fresh milk and cool it before adding it to the dough. This can be a real pain. Notwithstanding this advice, I saw a Vito & Nick's video some time ago and it showed the owner pouring milk out of a jug. Milk is also expensive and it may be cheaper and more convenient to use whey (a heat treated form) if it is browning of the crust that is desired. In Pizza Hut's case, they went to frozen dough and, in so doing, it jettisoned the dry milk powder and dry buttermilk powder.
If you are interested, this is a pretty good PMQ Think Tank thread on the subject of use of milk in pizza dough:http://thinktank.pmq.com/threads/milk-in-dough.407/
Papa John's avoids the kinds of issues involving the use of milk products or whey by using a lot of sugar in the dough. So, there is plenty of sugars available at the time of baking to contribute to crust coloration. But at the risk of people, like Tom's wife, who may find the crust too sweet.
As an aside, Donatos also used to use fresh eggs. It still lists whole eggs in its ingredients statements but it is not clear whether the eggs are fresh or dried (the milk they now use is dry milk). Years ago, they touted the nutritional and healthful effects of fresh milk and eggs but stopped using that strategy somewhere along the line--maybe when eggs fell out of favor because of their alleged high cholesterol content and whole milk was frowned upon because of its high fat levels.