First there is this Wikipedia article about OpenFormula where the following bit of history can be read:
"In 2005, Microsoft's Brian Jones noted that OpenDocument did not define spreadsheet formulas in detail (Jones, 2005). However, at the time Microsoft's competing proprietary XML format also did not include this kind of detailed specification for formulas (Wheeler, November 7, 2005).
Microsoft continued to protest that OpenDocument could not be used because it did not define a format for spreadsheet formulas, yet its own specification continued to omit any specification about formulas through April 2006. Finally, in May 2006, Microsoft also began defining formulas in its XML format, 15 months after the first version of OpenFormula and 3 months after OASIS posted its first official draft of its specification."
Next, VML is "deprecated" in OOXML, but it is still being used.