Why are there few accessibility options in Digital Editions?

I have a client with Irlam's Syndrome which means she needs a lot of access support. She needs to be able to do the following:-

• change background colour of the book page
• have text to speech by using MAGic 14

Both of these options are not available to her in Digital Editions which she is being forced to use as of 31st October  Dawsonera are having to change from Adobe Acrobat Reader ( which has these functions she needs) to Adobe Digital Editions which supports EPUB formats and doesn't have the above options. Unless someone can tell me different.