But these days talking books for the blind,... The use of 'but' rather than 'however' is, in these terms, more engaging with the reader; the phrase 'these days' is an informal one- it has no specific reference
other ideas are providing- normally not used in the progressive form formally, so it's another example of making the text more familiar.
This is not a very heavy academic written text, so I'm not sure that it provides enough to show very much- the use of 'used to be written' instead of 'people used to write' doesn't persuade me that there's much going on here in these terms. It's a text that you might see in an academic context, but that doesn't make it an academic text, IMO.
However, I must declare a bias- I can't stand Deborah Tannen; I think she has based her career on anectodal and poorly analysed coffee table examples that she has tried to extend into a theory based more on preconception than fact.
- For Teachers