I read that as the top 20 Blu-ray titles sold 12% of those same 20 titles combined on DVD and Blu-ray, but the actual top 20 DVDs only list would of course have different titles. Batman Begins was released 2006 on DVD and this list compares the new Blu-ray release against a sales of two year old DVD title. I don't know the DVD vs BD release dates of the other 19 titles, but at worst case this list has the current 20 biggest Blu-ray movies against 20 random DVD-titles (of course the list isn't the worst case, but you get the picture). Batman alone screws the marketshare numbers quite a bit.
You are probably right, but I'm not sure the top 20 list would be all that different. Batman Begins was just also released in a special edition pack for DVD. While that might not make it a #1 DVD title for the week I'm sure it managed top 20 as I don't think there was anything remotely big out on DVD last week (well almost 2 weeks now). Blu-ray accounted for 7.3% of sales in $, meaning probably 5% or less in volume.
But I'm not sure what this discussion is even doing in an NPD thread.