I've never taken the name "Unmanned Spaceflight" in an absolute literal sense, and it surprises me to find the name being offered as the basis for a criterion for topicality. I've been around long enough to remember when this board was not called "Unmanned Spaceflight", and when its focus was the two MERs. Then Cassini was added, and other missions. My memory is fuzzy as to when the name "Unmanned Spaceflight" was born, but it was not suggested at the time as far as I recall that the name change meant a radical change in the scope of the forum.
After all, if we are to lean on an excessively literal interpretation of the phrase, then MERs and Phoenix would have to be ruled out ever since they landed on Mars. They do a lot of interesting and important things there -- but flying through space isn't one of them. As for the "manning", well, there's an awful lot of people involved in controlling the vehicles and collecting the data!
As far as the topics which one might expect to find in a discussion that was actually about unmanned spaceflight -- say, the physics of orbital transfer, or rocket engineering -- there's not a lot to be found here, and there's no specific forum for discussing them. Which makes me surmise that the forum isn't really about unmanned spaceflight at all.
What it's mostly about, as far as I can see, is the discussion and manipulation of accessible science data -- particularly image data -- from devices which either are flying through space, or which once were flying through space, or which do their flying through space by sitting on the ground on a planet. In which case the primary difference between Keck and Cassini is in the quality of the images. To which it seems to be added that the data must contain information about natural objects within the bounds of the solar system (however far they extend).
I've got no problem with this being a planetary science data discussion forum, or even a solar-system-only planetary science data discussion forum. I'm perfectly comfortable with that. But I just don't see how it's true that those limitations follow from, or are even related to, the notion of "unmanned spaceflight". And if it is, in fact, a solar-system planetary science discussion forum, then trying to shoehorn discussion into an "unmanned spaceflight" shoe could have unwelcome consequences.
For instance: Uranus has not been a target of unmanned spaceflight since Voyager II. There are no current plans to send a probe to Uranus; from what I hear, it's unlikely that there will be such a probe this century. (A fact which wounds me deeply.

) According to the way policy is apparently being presented here, if Hubble or any other telescope happens to discover something interesting about Uranus -- moons, rings, weather patterns -- it won't be topical because Uranus is not a plausible target for unmanned spaceflight. On aesthetic and practical grounds alike, that seems to be an unfortunate conclusion to come to -- especially if the primary basis is to maintain consistency with a name. (It would also be surprising, given that the forum contains a section specifically devoted to Uranus and Neptune -- but then sections have been ruled 'marginal', or even shut down, before now.)
On the other hand, if solar system science is more generally topical here, then a case can certainly be made for discussing data from other planetary systems at least insofar as it sheds light on the origins, construction, or composition of our solar system.