Although this incident is true, but it was specific to the battle of Bader. So you can generalize this to all battles because in the Quran there are verses that mention war prisoners:

- Feeding war prisoners:
>And they give food in spite of love for it to the needy, the orphan, and the captive http://quran.com/76/8

- Replacing war prisoners with money:
>So when you meet those who disbelieve [in battle], strike [their] necks until, when you have inflicted slaughter upon them, then secure their bonds, and **either [confer] favor afterwards or ransom [them]** until the war lays down its burdens..... http://quran.com/47/4

- Hadith in [Muslim][1]
>It has been narrated on the authority of Anas b. Malik that eighty Persons from the inhabitants of Mecca swooped down upon the Messenger of Allah (ﷺ) from the mountain of Tan'im. They were armed and wanted to attack the Prophet (ﷺ) and his Companions unawares. He (the Holy Prophet) captured them but spared their lives. So, God, the Exalted and Glorious, revealed the verses:
" It is He Who restrained your hands from them and their hands from you in the valley of Mecca after He had given you a victory over them."



Also in many historic events, freeing specific war prisoners in battle of Bader because they used to help Muslims, if a war prisoner knows how to write and read then he will be freed after teaching 10 people, or killing some if they were really bad, such as killing brutal people of Quraish for hurting the Muslims...


  [1]: http://sunnah.com/muslim/32/162