This is a good debate, and highlights the importance, when writing rulebooks, to use commonly agreed-upon terms. The problem we're having is, ultimately, that the description was written in English, not D&D Rulespeak.
I'd heartily suggest, since you're going to do this anyway, that you simply decide the way it's going to work for your game, and make sure you tell players before they purchase such a ring so they know exactly how it will work.
But, for argument's sake, by all means let's continue the debate.
Earlier I stated that, strictly speaking, rules-wise, it shouldn't apply to an area-of-effect spell. However, upon re-reading the ring description, it does SPECIFICALLY say that the ring functions exactly as a counterspell action. To use the Counterspell action does not require that the spell be targetted upon you. Strictly speaking, the counterspell action doesn't even require you to be in the intended area of effect of the spell. However, the wording of the ring description leads me to believe that, should you be in any way within the area of effect of a spell, the appropriate spell will be withdrawn from the ring as a counterspell action - i.e., the original spell will simply not go off, just as if you had readied an action to counterspell it. The advantages of the ring are that you don't even need to know that the opponent is casting the spell - the ring takes care of it.
I don't think this overpowers the item, since, honestly, the odds of being hit by the exact spells with which you've loaded the ring are pretty slim. And you can't change your mind and swap out spells it contains! So if you stick a few fireballs in it, and you realize you're going up against a cult of lighting wizards, you're just out of luck.