In the UK the probation period is effectively meaningless. Until you've been with an employer for 2 years, you don't have any rights to an employment tribunal, except when the dismissal is "automatically unfair" (eg discrimination due to sex, race, disability etc).
Yeah I know someone who used to do employment tribunals. She says it's a ridiculously high standard and most employers are not that dumb. She'd only really take cases where they haven't paid their wages and the employer was a mess. The amount of pregnant women that would come to her and she just couldn't help.
That's what's known as 'at will employment' in the U.S. A lot of states have it. They can fire you for anything that doesn't violate civil rights and it's pretty easy to fire someone because of their race and claim it was for another reason.
While I'm oversimplifying, basically 49 out of 50 U.S. states are at will employment. (A majority have public policy exceptions, and only 3-4 have NO exceptions.) Montana is the only U.S. state that is not at will (after a probation period).