Prior to Excel 2007, the resulting HTML was horrible to modify, because it contained a large amount of
extraneous information that could be used to “round-trip” a worksheet through the HTML format.
Round-tripping through HTML never worked well, always lost data or formatting, and was almost
never used. With the introduction of the XML file formats in Excel 2007, the requirement to round-trip
through HTML no longer exists, and the Save to HTML feature has been redesigned as a simple publishing
mechanism—resulting in much cleaner HTML.