It has been a long tradition to use tables to control the layout of an HTML document. However, tables were the only tools for the purpose of laying out an HTML document, and designers have very little control.
Unfortunately, screen readers interpret tables in a linear fashion, and that can cause major confusions for users who rely on screen reading. To sighted users, a vertical column of links is read top-to-bottom with minor problems. However, a screen reader reads a table row-by-row. As a result, the presentation of available links to a visually impaired is very different from that to a sighted user.
A typical web page use an overall table to control the overall layout of a web page, most of the time in to top, left, middle and right portions. Then, an embedded table in the left portion specifies links. Reading a table within a table can be quite confusing.