Well, death penalties in the US or other places aren't held in the town square. Nor are people physically forced by the police to watch in order "make an example"
They are held in a public square to show that execution is real and that if you take the life of another person this could happen to you.
In the majority of the countries in the Middle East they are announced in the Mosques after Friday prayer to make sure that eveyone is aware that its going to happen. This could be seen as a way to make sure everyone goes to watch or to make sure people leave the area so they dont witness it. When you think about the thousands of people who could live in the area its impossible to 'physically force' everyone to go and watch them.
Also the families of the 'victim' normally has the final say on this - if they wish to pardon the person then they will not be executed, that certainly isnt the same as the USA.
Please dont take misunderstand my comment - I was simply explaining why the beheading videos didnt upset me as much as the Tidal Wave hitting Japan did.