Please. Most books and articles don't mention accessibility at all. Accessibility is important but is it really as important as understanding http or other main line topics?
Doing the site first then accessibility second usually either means accessibility simply doesn't get done at all (since people forget and/or priorities change before it is done), or it is retrofitted in a really half-assed way.
This is really important stuff (both legally these days in many countries, but also ethically) so giving it second-billing is probably a mistake.