Byron, there are chemicals such as Ammo-lock that do what you said (detoxify ammonia, chlorine and chloramine) without mentioning nitrite and nitrate, but I don't believe Seachem Prime actually ADDS anything additional in order to detoxify nitrites and nitrates. According to their website, the formula wasn't designed for nitrite and nitrate removal, but it just happened to do so at elevated doses:
Q: How does Prime make a difference in reducing Nitrates?
A: The detoxification of nitrite and nitrate by Prime (when used at elevated levels) is not well understood from a mechanistic standpoint. The most likely explanation is that the nitrite and nitrate is removed in a manner similar to the way ammonia is removed; i.e. it is bound and held in a inert state until such time that bacteria in the biological filter are able to take a hold of it, break it apart and use it. Two other possible scenarios are reduction to nitrogen (N2) gas or conversion into a benign organic nitrogen compound.
I wish we had some more "concrete" explanation, but the end result is the same, it does actually detoxify nitrite and nitrate. This was unexpected chemically and thus initially we were not even aware of this, however we received numerous reports from customers stating that when they overdosed with Prime they were able to reduce or eliminate the high death rates they experienced when their nitrite and nitrate levels were high. We have received enough reports to date to ensure that this is no fluke and is in fact a verifiable function of the product.
Seachem. Prime FAQ
I don't know if Prime does actually have more chemicals than Ammo-lock, or if API simply didn't conduct the necessary studies to say that their product also detoxifies nitrite and nitrate. But then again, I just checked out Seachem's product line again as I'm typing this and saw that they carry a product similar to Ammo-lock called AmGuard. The only differences that I'm seeing between Prime and AmGuard (aside from Prime detoxifying nitrite and nitrate) is that Prime also detoxifies heavy metals and provides slime coat. Now I'm wondering if it's the chemicals included for those that are mysteriously detoxifying nitrite and nitrate. I agree that it's best to add as little chemicals as possible, I just thought the above response from Seachem was interested.