Such sociobiological arguments are generally wrought with problems.
But, it does actually make sense that a correctly thrown and landed punch would generate a higher transfer/concentration of kinetic energy upon impact as compared to an open palm strike due to the rigidity of the structure.
Like you said though, accuracy is the primary issue and targets can move suddenly and unexpectedly during combat. So, it's really a judgement call that each of us has to make based on our own training, physicality, and the opponent. If you are slight framed, then palms might be a better option. If you have thick dense bones, then punching may be better.
Finally, regarding boxers fractures, much of those are the result of:
A) people with little to no actual fighting skill (accuracy, timing, technique, etc...)
B) people with skill but who become overly dependent on their protective gear (wraps, gloves, headgear, etc...) and thus never really develop the strength in their supporting structures or even really learn proper bare fisted punching mechanics to begin with.
C) bad luck, as again sometimes Murphy and his Law butt in at just the wrong time
Just my two cents.