As monktim says - in this particular case it serves no purpose. You'd use that form to limit the rows that are updated, or fetch data with which you wish to update the target table with a join, like this:

update the_table
   set col1 = t2.col2
  from the_table t1
     , other_table t2
 where t2.id = t1.id
   and t1.somecol = "some value"
   and t2.anothercol = "some other value"
[download]

Having used Sybase for 15+ years I'm really used to this syntax, and I find it quite powerful (and you can do the same thing with DELETE of course).

Michael