There is currently a bug defect entered against this behavior. I do not have a date for when it might be fixed. For the submitted data in the View Responses tab, you can format columns that contain numbers to display the missing comma delimiter. In the View Reponses tab select the column with your numbers. Click on the Table button in the toolbar (third from the left). The table formatting tools should now be displayed. Click on the tool labeled "1,000". This should format the selected column (or cell) to display the number in the format you are requesting.
Software Quality Engineer
Adobe Systems, Inc.