Yes, Office 2013 is at last able to write "strict" Files. Office 2010 and 2011 (which is the latest version for Mac) are not
According to whom? Office 2011 was promoted as being the first software to meet the strict standard, followed shortly by Office 2010 service pack 2.
- and yet the support for ODF was removed in these versions!
ODF support was never included in Office 2011 for Mac. A good level of ODF support was included with Office 2010 and was carried forward with Office 2013. ODF support was never removed from any Microsoft Office product.
The only reason for this is - once again - that MS is trying to push it's own standards... Or can you think of any other motive to remove support for an ISO-approved, open, and actively developed standard, while still maintaining support for much older, proprietary formats?
Your assertion that ODF support was removed from Microsoft Office is false.
As I already stated, although ODF is an open file format that is backed by an open standard, the ODF format was replaced by OOXML. There's not much point in adding support for older technologies when the world has by and large adopted its replacement.
Beginning with Office 2007 Microsoft adopted the Office Open XML standard as the default file format for Word, Excel and PowerPoint replacing proprietary DOC XLS and PPT file formats with the current open format.