The problem here is that there is no way to cleanly detect a conflict. The documentation talks about pages which have changed, but a page changing isnt a good indicator of conflict. A conflict can happen due to a read conflict. E.g.
Update Customer Id: "UPDATE Customers SET id='bar' WHERE id='foo'; UPDATE Orders SET customerId='bar' WHERE customerId='foo'"
Add Customer Purchase: "SELECT id FROM Customers WHERE email="blah"; INSERT INTO Orders(customerId, ...) VALUES("foo", ...);"
If the update task gets committed first and the pages for the Orders table are full (i.e. inserting causes a new page to allocated) these two operations dont have any page conflicts, but the result is incorrect.\
In order to fix this, you would need to track the pages read during the transaction in which the write occurred, but that could easily end up being the whole table if the update column isnt part of an index (and thus requiring a table scan).