I should have said "If there is a clustered index on the table it will return the data in the order of the clustered index"
That's not always true however. Just because a table has a clustered index it does not mean a query without ORDER BY will return rows in that clustered index order - even if there are no other indexes involved. If SQL Server chooses to do an Advanced Scan or Unordered scan then rows may not be returned in the clustered index order.