Printing and distribution costs on hard copy books far exceeds 50% of the current cost. Publishers would be making far more money paying Apple the 30%.
That is absolutely false. PB&D (Printing, Binding & Distribution) for textbooks are usually in the 10-15% range of retail cost.
The vast majority of the costs for books is in the editorial costs, permissions for text and photos, overhead, and profit.
At least in the K-12 space, a 30% cut to Apple will be non-tolerable. Just doesn't work for the current business model and market.