hotsh/rstat.us — comment on commit 0486e6c5a42bf63304473f4749a57746fcbb0ccb
File: app/models/update.rb line 270
By wilkie:

Just need to check the last update so that somebody doesn't accidentally double post. It's fairly obvious that this was the intent as the last_update field exists to mitigate the need to query the last update somebody made. We certainly don't want to check every status somebody has ever made! That would be awful.

Not including the author id check is only bad in the situation where somebody posts another's status to their feed that is exactly like their last status. That isn't possible currently, but maaaaay be a vastly improbable situation in the future.

I wrote that line. It says "This update came from the same person, says the same thing as the last post, but isn't the last post..." That's the strongest logic possible, but you could weaken it and be ok, but certainly not just to simplify the code. :)