That site suffers from self-selection bias. It is therefore statistically meaningless. Fun, but meaningless.

For another example of this problem, take a look at The Linux Counter. This site has been going for 18 years in various forms, it has gotten national magazine press several times, and unlike this shutter activation site, its users are almost certainly all happy Linux users. Yet, right on its front page, the top-level stats are clearly very odd:

• more users registered than machines

• that in a world where a Linux sysadmin is likely to be personally responsible for more than one machine, sometimes dozens or hundreds

• a guess four orders of magnitude higher than the measured value

• doesn't jive with measured evidence, such as the ever-controversial Netcraft stats, which has the great weakness that they only count public-facing web servers and can be confused by proxies, so they greatly undercount the actual number

For those who think I'm getting away from your actual question, I'll spell out the application:

• measurement beats out self-reported stats every time

• accurate measurement is often difficult

• those in a position to do accurate measurement often have poor incentive to release the results publicly

• in the end, experts' guesses might well end up being closest to the actual truth