Hi Doug --- good question. Duke's earlier lessons (Blues A Rama & Swingin the Blues) are in Flash, so they don't work with the iPad, iPhone etc.
Apple may choose to support Flash at some point --- but I have not seen anything concrete about it. We will also likely update those lessons, but probably not for another year (we want to get our new tab / chord system fully polished before doing the switch).
For now, my recommendation would be to use your PC for theses lessons. You can also print out all of the chords / tab for these lessons if you want off-line access.
I agree --- there is a huge amount of beautiful music in those lessons!