I think the trend you describe could be put in terms of disintermediation of web properties. Facebook, for instance, tries to be a platform that does everything. But much like real life, products are beginning to specialize because niche products can just do a better job at meeting the needs of a segment. That's why I disagree with you that this is just a trend.

Point taken. I would still argue that most people would not go to bare post composer to write. Personal blogs and websites fill this space. Of course, there are lots of those, who like minimalistic and distracion free environments.