I'm thinking they're higher than that. A big part of that 6% figure comes from their estimate that Amazon has 90% of the ebook market, which seems really high considering Apple and B&N both claim a 20% share. Also, there's this information from Publisher's Weekly. Dollar-wise, reported ebook sales were only 20% less than paperback sales in July. If that 6% figure is accurate, then sales shouldn't be that close.
Here's the link to the PW article.
E-book Sales Jump 150% in July