GenealogyinTime examines the popularity of genealogy

You occasionally read claims like "Recent surveys have found that genealogy ranks as the second most popular hobby in the United States." That's a blog post from Ancestry, it strains credulity.
There may have been 200 people at Saturday morning's BIFHSGO monthly meeting, but that's once a month. What's more popular? How about reading? The Ottawa Public Library circulated over 950,000 items per month during the third quarter of 2013.
Now GenealogyinTime online magazine has examined the evidence and taken a hard look at the facts dispelling some common myths and misunderstandings about the popularity of genealogy.
The article points out the importance of distinguishing between various levels of interest, from those actively conducting family history research up to the larger group of those with a general interest in ancestors.
Based on an assumption that one person in 40 in a family actively conducts family history research, somewhat debatable, the number of people involved in different English-speaking countries is calculated: US: 7.9 million; UK:1.6 million; Canada: 0.9 million; Australia: 0.6 million; Ireland: 0.1 million; New Zealand: 0.1 million. 
The article then examines the number of daily visitors to the top 10 genealogy websites, collectively about 113,500 visitors a day, and internet traffic to all genealogy websites very close to 300,000 visitors per day.
Using another bold assumption about the frequency with which genealogy sites are visited GenealogyinTime estimates that there are about 2.1 million people in the major English speaking countries who are active (online) in genealogy.
I'm wondering what error bars should be put on this estimate? It's certainly rather at odds with the following claim by Ancestry.

Ancestry.com is the world’s largest online family history resource with 2.1 million subscribers across its Ancestry.com branded websites. The company has approximately 2.7 million subscribers across all its websites, including Archives.com, Fold3.com and Newspapers.com.