The iPad Mini is actually about as powerful as the iPad 2, and when it comes to iBooks that is something of a problem. Neither tablet has the horsepower to adequately display the latest Epub3 features which Apple added in the iBooks 3.0 update.
In particular I found that my iPad 2 could not display the equations found in a demo Epub3 ebook (here). Page turns and general app performance was also laggy while trying to read that ebook on Matrix Algebra, and that limitation was shared by the iPad Mini.
I can understand that most people won't care about the problems surrounding a niche use like textbooks, but this is an issue which is only going to become more important as time goes by.
Apple is likely going to push the iPad Mini into schools, and as more students use them to display iBooks textbooks the issue with MathML will grow to be a serious problem. What's more, I would not be surprised to learn that the MathML issue is only the tip of the iceberg. I would bet dollars to donuts that students will encounter other problems in their enhanced textbooks, and I would also bet that later updates for iBooks only makes the situation worse as Apple adds more support for Epub3.