Deleting rows from tables without FK relationships
Your example would allow for the cascading delete that a cascading delete foreign key would.  But I would argue that a foreign key does much more than facilitate simple cascading operations.  Borrowing from the documentation on FOREIGN KEY Constraints:


  A foreign key (FK) is a column or combination of columns that is used
  to establish and enforce a link between the data in two tables.  You
  can create a foreign key by defining a FOREIGN KEY constraint when you
  create or modify a table.
  
  In a foreign key reference, a link is created between two tables when
  the column or columns that hold the primary key value for one table
  are referenced by the column or columns in another table. This column
  becomes a foreign key in the second table.
  
  For example, the Sales.SalesOrderHeader table in the
  AdventureWorks2008R2 database has a link to the Sales.SalesPerson
  table because there is a logical relationship between sales orders and
  salespeople. The SalesPersonID column in the SalesOrderHeader table
  matches the primary key column of the SalesPerson table. The
  SalesPersonID column in the SalesOrderHeader table is the foreign key
  to the SalesPerson table.
  Blockquote





  Although the main purpose of a FOREIGN KEY constraint is to control
  the data that can be stored in the foreign key table, it also controls
  changes to data in the primary key table. For example, if the row for
  a salesperson is deleted from the Sales.SalesPerson table, and the
  salesperson's ID is used for sales orders in the
  Sales.SalesOrderHeader table, the relational integrity between the two
  tables is broken; the deleted salesperson's sales orders are orphaned
  in the SalesOrderHeader table without a link to the data in the
  SalesPerson table.
  
  A FOREIGN KEY constraint prevents this situation. The constraint
  enforces referential integrity by guaranteeing that changes cannot be
  made to data in the primary key table if those changes invalidate the
  link to data in the foreign key table. If an attempt is made to delete
  the row in a primary key table or to change a primary key value, the
  action will fail when the deleted or changed primary key value
  corresponds to a value in the FOREIGN KEY constraint of another table.
  To successfully change or delete a row in a FOREIGN KEY constraint,
  you must first either delete the foreign key data in the foreign key
  table or change the foreign key data in the foreign key table, which
  links the foreign key to different primary key data.