"flag" for case/adposition

[nigel Vincent]

Just a quick query re Martin's endorsement of Zwicky's observation that 
  "Everything you can do with adpositions you can do with case 
inflections, and vice versa." Might suffixaufnahme or case agreement be 
an instance of something you can do with case but not with an 
adposition? What too about case attraction (arguably a kind of case 
agreement - cf a paper by Hans Vogt many years ago)?
Nigel