The issue with trying to be dyslexic-friendly is that it's quite a subjective condition - meaning that improvements are different for each person who suffers with the condition rather than there being established rules to abide by.
For instance; some dyslexic users like to reset the whole site to black and white, others like to set the text much larger, some have preferences for one particular font... I've even met a dyslexic user who has to set their font to darker grey on a slightly lighter grey background (which is great for them, but terrible for almost everyone else).
Because there is no standard dyslexic-friendly criteria to follow (unlike colourblindness and other visual impairments) you have to ensure that the sites you build follow well established web standards that will allow users to change the font styles, colours, sizes etc as much as they desire, rather than locking in the fonts and styles so they cannot be changed.
Stack Exchange could perhaps provide some different CSS styles that can be selected from an accessibility menu of some sorts - with a variety of font styles, colours and sizes to choose from. But again, what options do you provide? It's really just about providing a large degree of personalisation (which incidentally may also be something non-dyslexic people would appreciate).
So yes, as a concept I totally agree with you. We should be making the site as accessible to everyone, but making a site dyslexic-friendly is an incredibly difficult thing to achieve, because everyone is different.