I can't tell if you're being sarcastic or not. In case you're not, here's an example, from Germany, to disprove that all calendars start on Sunday and end on Saturday.

http://www.timeanddate.com/calendar/?country=8

Choose other countries from the dropdown and you'll see many, if not most, have the week starting on Monday and ending on Sunday.

The Abrahamic week did end on Saturday, which they probably got originally from the Vedic calendar as that is older and also has the last day of the week on a Saturday, but Constantine moved the sabbath to coincide with his existing sun worship, so since then the situation has been confused and so calendars vary on which day to end with. In the UK you can generally find both examples on sale if you shop around.

Is this why Saturday + Sunday is commonly known as the Weekend?

> Go look at any calendar [in the US] and you'll see they all end on Saturday.

Fixed your US-centricism there.