Thank you for the post.
You are correct that as of FileMaker Pro 13 "exporting to the .xls Excel file format is obsolete and any old script steps that exported data to that format are automatically exported in the .xlsx Excel file format."
If you would like to see this changed, I would encourage you to enter this as a suggestion into our Feature Requests web form at:
These web form suggestions are monitored and read by our Development and Product Management departments where they are then discussed and considered for a future release. Although I could copy your post and paste it into the web form, there are some questions asked that only you can answer.