Why are nested tables that bad

I am reviewing a web site using seven tables on each web page, one table having four nested tables, and two of these a nested table each.

I would like to give this web site very bad marks, but the problem is that the the tables linearizes well, the web pages sounds right in a screen reader like JAWS, and all the web pages look nice in more than 99% of the browsers in use today.

So what is the problem?

The truth could be, that just one misspelled word on the front page is a greater offence or what? Please give me the facts about nested tables. Why are nested tables bad in the real world of accessibility? Teach me a lesson!

Best regards,
Jesper