Views And Instead Of Update Trigger Limitation. Why?

I am attempting to use views and Instead of triggers to insert, update and delete rows from THE table that is exposed through a view. In my application, the views provide a filtered set of rows from the base table that a user has permission to access. To improve performance, I submit a set (i.e. multiple rows) to be acted upon in a single SQL Statement. The insert and delete triggers work great. But, for some reason, the Instead of Update trigger on the view will not accept multiple rows. The Error I receive is:

Msg 414, Level 16, State 1, Line 1
UPDATE is not allowed because the statement updates view "FooView" which participates in a join and has an INSTEAD OF UPDATE trigger.

The only hint I can find about this behavior is from BOL for the Transact-SQL Update statement:
"A view with an INSTEAD OF UPDATE trigger cannot be a target of an UPDATE with a FROM clause."

Why is this not allowed?

If the trigger is on a table and the update statement is executed against the table it works. Why is the statement not allowed to execute against a view that has exactly the same construction as the table?

Any help or explanations for this behavior is appreciated.

I've included a code sample that will replicate the behavior and problem.

----------------------------------------------
Code Sample:

CREATE TABLE Foo (
ID INT PRIMARY KEY,
aName VARCHAR (10),
aValue FLOAT
)
GO
-- The view and its triggers
CREATE VIEW FooView AS
SELECT [ID]
,[aName]
,[aValue]
FROM Foo
GO
-- Instead of Triggers on the view
CREATE TRIGGER FooViewInsertInsteadOf
ON FooView
INSTEAD OF INSERT
AS
BEGIN
INSERT INTO Foo
SELECT Id, aName, aValue
FROM INSERTED
END
GO
CREATE TRIGGER FooViewInsteadOfUpdate
ON FooView
INSTEAD OF UPDATE
AS
BEGIN
UPDATE Foo
SET
Foo.aName = Inserted.aName,
Foo.aValue = Inserted.aValue
FROM Foo
JOIN INSERTED on INSERTED.ID = Foo.Id
END
GO
-- Test the Insert Trigger
INSERT INTO FooView
SELECT 2, 'First', 2.0
UNION ALL
SELECT 3, 'First', 3.0
UNION ALL
SELECT 4, 'First', 4.0
GO
SELECT * FROM FooView
GO
-- Update a single row in the view. This works with the Instead of Update Trigger.
UPDATE FooView
SET
FooView.aName = 'Third',
FooView.aValue = 3.3
WHERE FooView.ID = 3
GO
SELECT * FROM FooView
GO

===============================
-- T-SQL will not support the following statement when executed against a view with an instead of trigger.
-- If this statement is executed against a table with an instead of trigger it works as desired.
-- Why can't I execute this against the view?
UPDATE FooView
SET
FooView.aName = tmp.f1,
FooView.aValue = tmp.f2
FROM FooView
JOIN (
SELECT 2 as [id], 'Second' as [F1], 2.2 as [F2]
UNION ALL
SELECT 4, 'Fourth', 4.33
)
as tmp on FooView.ID = tmp.[id]