>Contractually expanding it for a mutually agreed upon period doesn't strike me as that much different
As long as I'm compensated for that period (a normal wage) then I think it's fair.
Okay this is really bad, in the EU country where I live you usually first negotiate and sign the contract, then start working.
But the drawback is that it is really just done this way because the government requires that the business notifies it about your employment before you start working, which is a privacy issue.
I think I'd still prefer it the US way. I'd ask about this before starting to work. (if this isn't a no go)
You have to bring it up in the interview if you don't want to be bound by one. But even just asking could spook out the interviewees and get them to pass on you "Is this guy a Snowden? Is he going to steal and leak all our preeeeecious 'secrets'?"