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Im not sure but QTP datatable doesnt have same properties which excel has.
Here are differences:
1. DataTable is integrated with QTP Test Script, Excel App is third party resources to QTP. You can use both for data driven but when you give QTP Test Script to others you have to give Excel File without forget, where as datatable is integrated.
2. To me, I like Excel App because of flexibility, when you use datatable you dont have the same.
Ms Excel is Licensed software some may don't have this.So HP has created DataTable integrated with QTP which provides same properties as Excel.