@aL_ I think they are (rightly) worried about getting the user experience destroyed by opening things up too much, too fast, and as a user/developer of both WP7 and WP6, I think they are right. WP6 was frought with all sorts of well meaning apps and hooks that either killed the responsiveness or battery or both, and A---nd000d is the same way.
If an app were to be able to get integrated into a hub as you suggest (or as I think you're suggesting), the user experience would not be the same on all phones -- something that MS has time and time again tried to point out that they -- unlike some other googggly interfaces -- will do.
If you're looking for a totally open platform like some of the other guys, then WP7 is not for you. If you're looking for a strong, stable platform, with features like no other, with dedicated developers and users, LOOK no further.
@clody, note that these are "Beta" tools. They are not final. I myself was capable of driving the emulator Bing turn by turn directions using the GPS input from the tools, so that's pretty good, but if you have a better tool, no one is forcing you to use the built-in GPS tester.
Enjoy Windows Phone 7