Sachin defends his service Posterous because non-geeks can do everything with it without knowing how to walk and chew bubblegum.
I can't name five members of my immediate or extended family that has a lot of experience using a search based API. Hell, I'm a coder, and I don't have that much experience using a search based API.
I code when I hafta, and I don't want to write a whole set of libraries just to export my data. Creating artificial barriers to the exit door is the exact opposite of the spirit of Data Portability.
Edit: Incidentally, it isn't that I didn't read the API that thoroughly, it's that the API isn't that well documented. Pretty much what is screenshotted is what exists. It's not very well explained.