Yes this is correct. The primary difference in at will employment is that I also am not required to give my employer notice, whereas in the countries you mentioned I am.
You can as an employer walk away whenever you want, you just don't get the salary for the difference between the notice and when you left.
Example: if you have to give 30 days notice (very common in Italy) and leave on the spot, after your resignation have been accepted, you have to give the company the equivalent of 30 days of pay.
Which is exactly the money they should give you aniway if you stayed for the entire notice time.
But usually the employer and company find an agreement before coming to that.