I see (hat-tip Tim Bray) that Apple has released a new spreadsheet, Numbers, that looks very pretty. I think it brings out a couple of points about document standards too.
The first is that every time a new application comes out, it needs to have some new distinctive feature to sell itself. It may be simplicity, it may be beauty, it may be speed, it may be features, but there has to be a reason why people would want to buy it. If the distinctive be novel features, then there is every chance that the format will need to save data for that particular feature in new markup (e.g. a new namespace).
And as soon as we get to application-specific data, we have left the world of standards and guaranteed interoperability. Now this is a real problem for applications and catholic standards. (A little bird told me that Lotus won’t be adopting ODF as its native format for much this reason, and I haven’t seen Adobe Framemaker go native with ODF either. I would expect that the same is true for the delayed Mac version of Office with Open XML support: the problem being feature mismatch not format complexity per se.)
Which leads us into the world, not of guaranteed interoperability, but of graceful degradation.
It is interesting in the Apple promotional material that they say Numbers handily imports spreadsheets created in earlier Excel formats, as well as Excel 2007 documents created in new Office Open XML formats. I think this backs up a prediction I made recently, that no application can afford to ignore major formats for too long.