The success of that first comic took everyone by surprise and helped pave the way for the robust digital comics market we have today. (goodereader.com)
On the other hand, the North American digital comic market grew from US$ 500,000 to US$ 1 million in 2009 to US$ 6 - 8 million this year. (animenewsnetwork.com)
Of course, there are a lot of caveats to this, but it seems like a good ballpark figure for the current digital comics market. (goodereader.com)