Why doesn't update syntax match insert syntax?

I've been curious about this for a long time.  The syntax for an INSERT query is often much easier to use, in my
opinion,then the syntax for an UPDATE query.  For example, and this is what I am trying to do, assume you have a table
ofinner covers containing a name field and fields named x and y to track where each cover is, and you have another
tableof permissible locations for inner covers and other things, with fields containing the name of the stored item,
itstype, and its x and y coordinates. 

I am resetting my database to initial conditions, so I am putting the inner covers in their storage locations.  I've
alreadyupdated the storage location table, and now I want to update the locations in the inner cover table.  So I want
todo this: 

UPDATE inner_covers (X, Y)
SELECT sl.X, sl.Y FROM storage_locations sl where sl.name = inner_covers.name

If I were doing an insertion, that syntax would work.  But instead, I'm forced to do this:

UPDATE inner_covers
SET X = (SELECT sl.X FROM storage_locations sl where sl.name = inner_covers.name),
Y = (SELECT sl.Y FROM storage_locations sl where sl.name = inner_covers.name)

Or is there another, more convenient form of the UPDATE query that I'm not familiar with?

Thanks very much!

RobR