When you set 'this.datasource' in Application.cfc, the cfinsert / cfupdate tags still require a datasource attribute. It would make more sense for this attribute to be optional, as with cfquery, when a default datasource is set.
<cfinsert tableName="#this.table#" formFields="#my.fields#" />
ERROR: attribute datasource is required for tag cfinsert
This appears to be a parsing error since the error is thrown when the component containing the tag is loaded, not when the tag is executed.