Point well taken, but I don't think the sheer volume of comments is necessarily an indicator of the quality of the photo. A lot of people are in this to be part of a community of photographers, friends, and like-minded individuals. There is absolutely nothing wrong with that, but it is a different way of using the comments. You're right, it's hard to be top-notch everyday, no doubt. But personally, I'd still be happy to get suggestions. For me, learning is part of the enjoyment! But I do understand that not everyone feels that way.
One of the things they "taught" us in management classes was how to give feedback. Praise often and publicly, criticize sparingly and privately. Either way, be specific. People (employees, students, etc.) will naturally tend to do what garners them praise. Thus the "good" expands and crowds out the "bad" - naturally and generally painlessly.
That said - I, too, sometimes give out vague and gushy praise. I'll try to do better.