WordPress is still number 1 platform for blogging. Top used blogging functionality is blog posting and commenting to blog threads.
However, people that comment on a blog post normally have no way to get feedback eventually if anyone comments back in the same post. The post author (and administrator) receives notification for the comment but the comment author, on the other hand, has no natural way to be pinged back for a reply. This is a serious leak in the WP standard functionality. It is at least unethical not to inform someone for the reply (which might occur in a day, month, year even more).
WordPress comes with a standard feed for latest posts and feed for recent comments as well. However subscribing for all comments in a blog or finding a specific thread to subscribe for is not usable and not practical as well. The solution is the Subscribe To Comments plugin that adds a checkbox to the comment form which allows one to subscribe for further comments in the same thread. This is completely optional and up to ones preferences, but instead of breaking the whole conversation because of the 'echoing' this provides the instrumentation for a real communication.
WordPress.com uses Subscribe To Comments for 2 years or something, it's integrated in their web service. So why is it not included in the platform yet?