Yeah, I don't know. I've been using instagram sporadically since it started, and I think this article is about 18 months late. Over the last year or so there seems to be far more variation than this piece would suggest. While many might still be posting from their cell phones and using the in-built filters, I see an increasing number taking advantage of the improved quality of cameras in newer mobile devices and processing their images in Snapseed, Filterstorm, etc, to get results that are a bit beyond the nostalgic, retro thing (which Id say was the initial trend because it was the only way to get half presentable images from the then current in-built cameras).
Others upload film scans. Others pristine DSLR images.
Sometimes, I think it could be argued that for many, the whole instagram thing has little to do with photography at all.