Well, i would say from google or yahoo's perspective, 7.2% is negligible. Otherwise, wouldn't they support it for the apps you were referring to? I mean, we aren't talking about windows vs linux here, the differences between browser AJAX support and standards compliance aren't large enough that it can't be done without a separate development team.
The difference in compatibility between FF and IE (especially 6.0) is staggering, but they choose those browsers to support, and this decision is made with market share in mind, not standards compliance.
And i took the GPs point to be that the differences are minute, not non-existent.