User blog comment:Deshiba/Melee Supports Comparison/@comment-24058976-20140502042212/@comment-4022742-20140502193757

I grant you that Kayle is a support, and that she is melee. However she has a skill that makes her ranged 80% of the time, and after buying cool down reduction 100% of the time. So she plays like a ranged support and gets used like a ranged support by every summoner...

And exactly Nautilus's lack of interaction or beneficial boons to his allies is why he isn't classified as a sup. And is the only reason she IS classified as a support. The same way that Alistar was in that same class at a good portion of his LoL career.