Structural unemployment creates its own set of problems, doesn't it? It is not always heralded by technology changes because we do see this take place when, for example, manufacturing employees earning high wages find themselves without jobs when companies outsource their industrial operations to nations with lower labor rates.
The main problem with structural unemployment is that it is often tough to figure out what to do with a bunch of misplaced workers. Do you retrain them to do other things, show them how to adapt to new technologies or what? When you see high unemployment rates, that is often evidence you've got a lot of established workers who suddenly find themselves out of work.