Really? I'd have thought that tables, properly applied, would if anything be an aid to specialty readers...
Historically, the complete opposite tends to be the case, though newer screen readers have gotten rather better at parsing badly-formatted stuff. Regardless of which, a clean, well structured HTML document is always going to be far more accessible than a soup of nested tables.
Other reasons for avoiding table based layouts, especially nested tables, are the impact they have on page render speed. More often than not, they tend to require repeated recalculation of the page or complete retrieval of the page markup before the page can be laid out.
