This post is not primarily about spreadsheet formulas. Remember, Microsoft has produced hundreds of pages of "implementation notes" regarding their support of ODF and OOXML in MS Office. It is all useless for interoperability, IMHO, for the reasons given in this post.

But to satisfy your rhetorical question, table:formula is defined in ODF in section 8.1.3. This attribute is undoubtedly part of the ODF Standard. The behavior of Excel 2007 SP2 is to strip out all table:formula values from other implementations, unless they are written to Microsoft's specifications. This is taking a protocol approach to a data format, and demanding that documents magically adapt to MS Office and MS Office alone. Documenting this behavior is useless from an interoperability standpoint.

Thanks for the offer on the your session in Las Vegas. But I am familiar with MCE and it is not a solution to the above problem. MCE may be fine for specifying degradation of behavior to old versions of an application, such as when Office 2010 writes out a document with features new to that version, but also giving an alternative fall back representation for Office 2007. So it has some use for evolving schemas.

However, from an interoperability perspective, MCE doesn't cut it. MCE is really just hand waving and pixie dust. It just pushes the problem down one layer and leaves a more complicated interoperability problem to solve. Instead of just having to get implementations to support feature A, you need to rely on implementations to support MCE, as well as either feature A or its fallback B, and to support MCE, and A or B in an interoperable fashion. I think in most cases it is far easier to simply implement A in an interoperable fashion. And at best, if implementations do support MCE and A or B in an interoperable way, the implementations that support B but not A will receive a degraded experience and not A as the original document author specified. So in my mind MCE is an overly-complicated way of getting poor results.

If you are ging to be at the SharePoint Conference in Las Vegas net week then I'd be happy to have you attend my session on Markup Compatability Extensions (ISO/IEC 29500-3) where I'll talk about some of the challenges you identify above and some approaches to handling forward and backward compatability as well as round tripping of content through client implementations.

… unless it's got a festering sea of VBA inside it. Excel spreadsheets are the main culprit – many are just a place to put complicated BASIC programs – but Word is far from immune.

Well done, Microsoft – inventing text documents that can carry viruses!