I've been using a lot of them and found out I had to rebuild the same thing over and over again when moving from one company to the other, like localization management, user management, account management, database connectors, etc. This is what we do different, we provide tool so developers can build a RESTful API in a few days. It actually sits on top of Silex, a micro-framework for PHP.
The open data is coming from the cities that are open sourcing it. For now it's very limited I found. UK on the flip side was pretty impressive, the government is providing a feed for the whole country all in one place.
You actually have a pretty good point, I'll have to think about this to find a nice way to fix that. I'm sure you are not the only one to feel this way.