Despite the ability to set many of the style attributes of a cell containing a hyperlink, you cannot achieve the "changing" appearance of a simple hyperlink to mimic one created in Excel 2007.
I have added the changes to PHPExcel 1.7.9 to do that.
In short, the changes are to 3 files in writer/Excel2007;
writer/Excel2007.php, writer/Excel2007/Styles.php, and writer/Excel2007/Worksheets.php
If you include any hyperlinks on any worksheet, then the writer will emit the additional fonts and styles needed to achieve the Excel 2007 default behavior of a hyperlink. When the cells are emitted, if the cell is a hyperlink with no other style attributes,
then its style will be set to the "builtin" style for a hyperlink. The result is underlined blue text that turns purple after the link is clicked.
I hope you find this useful. The changes files are provided here: