«(...) the table generates a principal block box called the table wrapper box that contains the table box itself and any caption boxes (in document order). The table box is a block-level box that contains the table's internal table boxes. The caption boxes are block-level boxes that retain their own content, padding, margin, and border areas, and are rendered as normal block boxes inside the table wrapper box.
(...) The width of the table wrapper box is the border-edge width of the table box inside it, as described by section 17.5.2.»
coming from CSS 2.1, section 17.4 Tables in the visual formatting model
IE8, Firefox 3.6.8 and Opera 10.60 do not render a thick blue line while Chrome 5, Safari 5 and Konqueror 4.4.5 do.