The print media have general rules for expressing numbers. They are found in the Associated Press’ Style Manual.
Here are examples:
Spell out numbers under ten, use figures for over nine. Examples: "seven, eight, nine, 10, 11 and 12".
Always spell out numbers if they begin a sentence.
Use figures for ordinal numbers above ninth, and spell out under 10th. Examples: “Fifth, sixth, seventh, eighth, ninth, 10th and 11th”.
For large numbers, use following formats: 28 million or $28 million.
Never use Roman Numerals unless they are part of a name (e.g. WWII).
Spell out approximate numbers. Examples: “ a half million, about four hundred”.
In summary, it is the object of the print media to communicate numbers in a way that they read easily and clearly. Since the numbers are not being used in mathematical calculations, there is no need to write them in standard form.
Example: 3,002,381 people died from a certain cause last year.
Someone in the media who is trying to fix that certain cause would say over 3 million because it sounds like it could be a lot more than 3 million, and it's not a static number, so it will give people an idea of its growth.
It just kind of gets people to think about the numbers in the situation a little bit more.