> I don't see how third party developers are additive to Twitter
Then you're not in the community in which the third party elements(e.g. tweet aggregation, SSO login, fine grained access control) are vital part of. Which may be substantial, or not, and we as the sheep don't know.
You're right and I'm my sheepish hypothesis here is it's not substantial. I think twitter is largely a toy, if it were to completely vanish tomorrow, very little harm would actually be done to anyone. It's like a PMF question, does twitter have third party developers banging on their door with fists full of cash? No, they have a bunch of freeloaders that have built derivative toys.
Then you're not in the community in which the third party elements(e.g. tweet aggregation, SSO login, fine grained access control) are vital part of. Which may be substantial, or not, and we as the sheep don't know.