To define accessible, you must first define your target audience. Is it so horrible that someone is developing software for linux and isn't targeting some mythical 'computer illiterate grandmother' user?
However, having an abstract if you are going to present lots of information is definitely always good style. The scientific community require them on all papers - to help people decide if they should bother spending time to dig into the material or not. Not to make the material accessible for grandmothers.
And I think in the case of a complex piece of work like E17, that a simple 'what has changed since E16' list somewhere might help people who have already understood the Enlightenment way of working to get up to speed.
However, having an abstract if you are going to present lots of information is definitely always good style. The scientific community require them on all papers - to help people decide if they should bother spending time to dig into the material or not. Not to make the material accessible for grandmothers.
That is exactly what a good tl;dr provides.
EDIT: Fix borked sentence.