I think the motivations for blogging, from the two examples, cluster into three types: Selfless, social and selfish
Selfless - the outbound process. The contribution of own thoughts and research to the outside world. As Megan puts it “You put your work out there, not only to be discovered, but also to start finding your own voice”.
Social - the interactive process. The Web 2.0 value of social and collaborative learning. Blogging and responding seem to fit the Social Constructivist approach to learning.
Selfish - the inbound process, a validation process. Essentially, exposing research and ideas through blogging is likely to generate legitimate challenge or questioning which may enable corrective action. Better now, at what Catherine calls the “liminal” stage, than at the time of defending a PhD thesis!
All these are a positive addition to the closed and isolated world of traditional research where outside academic interaction is either absent or restricted to a narrow group of close associates.