The only thing constant is...
...change. Blogger API 2.0. Sigh. It looks like the future of blogging clients and servers is to have more code in if/switch/case statements and configuration options than actual logic. What's worse is a future where - despite all the interfaces being "open" - the only real guarantee you will have is that vendor A's clients will work with vendor A's servers. That's called vendor lock-in.
At the time the MetaWeblog APIs were written, I wrote this. Deja vu all over again.
IMHO, the right thing to do is to focus on the bits and bytes that go across the wire. Define an XML message for each interaction. In fact, divide the XML message into two parts - a header which contains "login" information, and a body which contains "post" information. Allow tool specific extensions through namespaces to support "filters", "actions", etc..