Surely this is down to the individual employer? Some companies try to add clauses like this to contracts here in the UK but thankfully they're generally not enforceable.
Speaking as an employer, what my employees get up to in their own time is their business as long as they get their work done when they're supposed to.
In theory, yes, In practice, nearly every single US employer has this somewhere in their contract automatically by default -- the only way a company doesn't, is if someone explicitly got it removed.
Also, in much of the US, the clause is enforceable, so companies have basically no incentive to remove it.
Count your blessings, every US and Canadian work contract (hell, even some contracting/consulting agreements) I have ever seen or signed had a no-compete and a clause prohibiting you from doing anything else than working for your employer.
Speaking as an employer, what my employees get up to in their own time is their business as long as they get their work done when they're supposed to.