If you count all coins (meaning any date), yeah the 69s outnumber the 70s. But in recent years, no, it's the other way around. There are many more 70s. It varies from coin to coin of course as to just how many more. But there are several cases where 80-90% of all coins submitted were graded as 70s. As to where I get the numbers, from the pop reports published by the TPGs. And from articles in the numismatic press.
This is actually a misconception. A 70 is not a perfect coin. A grade is actually a range of conditions. Just like there are low, mid and high range MS 64's the same is true for 70's Since a perfect coin is only theoretical, this is the only thing that makes sense. The 70 grade "range" goes from very close to perfection, to the theoretical, but unobtainable absolute perfection.
The same thought occurred to me, and I don't fully remember the argument he used to support his theory. For all I know, it could have been a clerical error. Either way, his grader of choice is now ICG.