Shortly after ARB's launch I collected the results of my mining grind (several hundred) and did some analysis to see if the results matched the stated probabilities for high quality finds. I got a 95% confidence level that the results DID NOT match (which is unfortunately not really that high).

With only 95% confidence I can't say too much, but based on that an my observations I think something is up with those numbers. I doubt their random number generator is at fault. If I had to guess I would say there are factors that affect success that are not represented in those numbers. Maybe some kind of 'biorhythm' affect or weather...

The fact that the game uses so much RNG to stretch out content is another topic altogether.