That appears to be his personal anecdotal experience and admits that figure doesn't apply to mobile.

And in my experience NAT traversal never works in the Philippines (I assume Skype was using a relay server).

This 2008 source says we don't have quantifiable data on the success rate.

ISPs don't have an incentive (note: 'shelby' is me) to allow you to run a server on your asymmetric bandwidth consumer internet downloading connection, unless the market demographics demand it (i.e. probably only in the developed western world). Thus the success rate is likely to get worse over time, not better as we move towards the global police state and top-down control over the internet. Moving to mobile should help accelerate the asymmetry of the internet, handing the power to our overlord masters.

Note this may also impact the way many crypto-coins are currently coded for P2P interaction, but I haven't studied their sources.