Lies, Damn Lies and Statistics
Yes I do know that these statistics have flaws, so I have tried to analyse them here and look at their validity.
The raw data from the Lifestyles survey is not available, only tables of probabilities. This wouldn't effect averages, but it isn't a very reliable prediction of the probability of extremes.

Penis Length
These statistics do seem to make sense.
It's more or less a standard distribution, with a very large peak at the average. This implies that most (about 75% of) men will be Mr Average, when it comes to length.

The average is 5.88", however the nature of distribution means the average is not the same as most common. This is because the few very long ones, bias things. So the median is 5.65". That's the point where 50% will be larger and 50% smaller. It's the typical size.
 Length % of men 3.50" to 3.75" 0.2 % 3.75" to 4.00" 0.3 % 4.00" to 4.25" 0.2 % 4.25" to 4.50" 0.7 % 4.50" to 4.75" 0.8 % 4.75" to 5.00" 2.0 % 5.00" to 5.25" 9.0 % 5.25" to 5.50" 10.8 % 5.50" to 5.75" 24.3 % 5.75" to 6.00" 23.9 % 6.00" to 6.25" 9.3 % 6.25" to 6.50" 6.7 % 6.50" to 6.75" 4.4 % 6.75" to 7.00" 2.9 % 7.00" to 7.25" 1.0 % 7.25" to 7.50" 1.0 % 7.50" to 7.75" 0.9 % 7.75" to 8.00" 0.8 % 8.00" to 8.25" 0.3 % 8.25" to 8.50" 0.3 % 8.50" to 8.75" 0.1 % 8.75" to 9.00" 0.1 % Source: Lifestyles Condom Co., 2001
Penis Circumference

The statistics here don't seem to fit any sort of standard distribution. There is a fair peak at just under 5" and the numbers fall away quickly below 4" and over 5.5". 85% are in this range.
The average is 4.97", however the nature of distribution means the average is not the same as most common. The median is 4.67". That's the point where 50% will be larger and 50% smaller. It's the typical size.

Some clever person has suggested that some of these measurements were taken to the nearest half inch, rather than quarters. This would explain the strange distribution, but doesn't significantly change the averages.
 Circumference % of men Under 3.00" 3.3 % 3.00" to 3.25" 0.4 % 3.25" to 3.50" 0.9 % 3.50" to 3.75" 1.1 % 3.75" to 4.00" 4.7 % 4.00" to 4.25" 6.3 % 4.25" to 4.50" 17.1 % 4.50" to 4.75" 11.7 % 4.75" to 5.00" 24.1 % 5.00" to 5.25" 9.9 % 5.25" to 5.50" 11.5 % 5.50" to 5.75" 3.0 % 5.75" to 6.00" 3.9 % 6.00" to 6.25" 0.5 % 6.25" to 6.50" 0.5 % 6.50" to 6.75" 0.1 % Source: Lifestyles Condom Co., 2001