Longer roasting raises pH (decreases acidity). See:
http://www.idosi.org/wasj/wasj2%285%29/17.pdf
Note that the initial time of small decrease of pH corresponds to under-roasted coffee, and coffee with this degree of roast would be unacceptable even to fans of light roasts.
Granted, I'm really lucky to live in PDX because we have such good access to great coffee it's made more noticeable. In my youth, I was actually of the same mindset until drinking a lot of different coffee and discovering my "misguided" way ;-)