So called hiking "rules" like the hydration rule just seem silly to me because they imply that hiking is some form of extreme physical activity when it is really just... walking. Come on; I mean, we're built for this. I imagine that both our evolutionary ancestors and our more recent ancestors were accustomed to working far more strenuously than the equivalent of what we consider a "strenuous hike," and on a daily basis. I also doubt that they always drank 26 oz. of water per hour.
There may be endurance athletes or extreme hikers who are really pushing the boundaries, but for someone who is in good shape I don't think that a little walking uphill would be putting us near the edge of our physiological capabilities.
For an interesting and somewhat related read, check out the book Why We Run by Bernd Heinrich. It's about running obviously, not hiking, but I think his approach applies to both. Also, you'll discover that he has some... um, non-mainstream views on the subject of hydration, which involve copious amounts of coffee and beer. All based on scientific experiment, of course.