This is a fascinating statistic, especially when we see that the income levels of the participants are 50% higher than the average.
Net Banks Gain One in Five Internet Households – 02.01.2008 – Bank Technology News Article
The survey of 1,032 Internet households found the average age of an direct-banking user is 47.8, with an average income of $99,200 a year – compared to the average online banking user who is 52.1 and earns $60,300 annually
Bankwatch 
Hrmmm… I could only wonder what the Canadian numbers are like.
It could go both ways in my opinion, since bank fees are generally higher here for the big banks (while even big US banks typically have feature-filled free accounts), but many CDN banks are being competitive with their interest rates.
I’d say that the average household income seen in the internet accounts is mainly due to the fact that it is obviously going to exclude those that cannot afford computers + internet access. As well, those with high account balances are far more likely to spend hours shifting their money around for an extra 0.5% APR.
Of course, in Canada, it is worth one’s time to switch to an online/direct bank just to save on the account fees, even if one doesn’t really have very many funds to actually deposit. So I’d assume we wouldn’t see the same disparity in income here.
Of course, this is a big worry for the US retail branch banks, whom will have to do just as much expensive off-line banking and carry smaller deposit volumes. And sadly, with their other concerns right now, it is probably not even on their radar.