Tumblrponies in RP or roleplaying blogs use the ask box to accept pieces of dialogue and story, rather than questions or instructions. RP blogs typically assume that a pony is submitting the message, and is speaking out loud the message's dialogue; they may also slip into a narrator role to describe current actions and events.
As such, this style of blog generally gives users a very strong say in what happens around the blog's main characters, but almost no control over what the main characters themselves say or do. RP blog owners also need to be very selective in the 'questions' they answer, to avoid causing discontinuities in their stories.
RP blogs should generally not be labelled as story blogs as well: RP adventures usually develop organically, rather than sticking firmly to a predestined story.