I prefer the teachers of guitar tricks overall, but as an Internet based service provider, from the customer's point if view, there is really no excuse to be so behind the times. It is not a matter of apple vs gt, it is the fact of the market and the kind of service you are providing.
You do not have to roll out a completely converted site all at once. But you do have to make the new and most popular lessons iPad/iPhone compatible so that your customers can see you are moving in that realistic direction. Otherwise, it's a dinosaur and will lose subscribers. Even on my laptop, the download pauses and breaks up. It just is not good enough.