Trial periods are pretty common in Europe, we call it "probation" in the UK but it is hard to objectively decide if someone is up to the job. If they are terrible or brilliant, it's not a problem but in the middle, I don't want to pay some new person £20K more than another dev just because they asked for it and aren't bad enough to be fired.
Until there is something quite objective about measuring performance against some kind of qualifications, then it is in danger of being more to do with personality than genuine value.
