From Halopedia, the Halo wiki
Again, there is no official source for all UNSC frigates having shields. Only Infinity's Strident-class escorts are known to have them. It's true that Marine armor is pretty resilient but the exact number of hits it can take is just part of gameplay. The books often show Marines getting killed attacks that wouldn't be very dangerous in the games (such as a single plasma bolt to the armored chest) yet surviving wounds that would kill them in gameplay.
The information you added was based on gameplay conceits. It was completely irrelevant to the article, which is written from an in-universe perspective. Check your talk page.