Well ont only is that stated in a book written in 2005 but it's also on pretty much every single website I check. They all mention you needing a basking spot of 90 deg. and a regular temp of 85 or so deg.
Even on the Caresheet for BP's on this website it says:
~80F (ambient temps)
~90F (basking temps)
Ball pythons do very well when heated from below (UTH = under tank heat). This can be achieved with heat mats made specifically for this purpose and found in most pet stores. Also available through online retailers is a product called Flexwatt, which is a thin sheet of heating elements that comes in a wide variety of customizable sizes.
And finally, overhead heat in the form of light bulbs or Ceramic Heat Emitters (CHE). A CHE screws into a socket like a bulb, but provides only heat without any light. These can be used as a supplement to a UTH to help maintain warm enough ambient temps.