No. Not copyright issues.
I think the publishing house are still grappling with the right approach.
To rely on advertisement and publish for free or to charge for the magazine?
For iPad, the route taken by most is to charge. A lot of application that are free for the iPhone, they are now charging for the iPad.
Paying for magazine is fine but not at the same price as the newstand price. I think they got the economic model wrong. Who is going to want to pay for an online magazine at the same price as one on the web? Delivery and manufacturing cost on the web is so so much lower than the actual published magazine.
But give them some time. Like ebooks it is now really picking up.. eMagazines will take some time too.