While I am more interested in the articles she refers to, Grandma's comments are interesting too. Take for example a recent post on the recent findings on Mercury by the MESSENGER probe (not only does Mercury appear to have an active magnetic field, but it also appears like it has volcanic vents!):
"Does the planet Mercury need to exist? - I mean in the business sense. Does it do anything? Or is it like those souvenir shells that persist forever on the mantelpiece? They have no use, but that's not the same thing as saying that they are not there for a reason. There is a difference between use and reason."
I like Grandma O'Leary. Everyone should have a grandma like her. That said, I don't think Mercury is "useless". To provide one possible answer, perhaps Mercury is there to increase our understanding of how the solar system and universe works and thereby employing many talented
One thing I must note from the referred article: why are astronomers always surprised that the solar system/universe is different than expected? The Voyager missions should have taught us by now to expect the unexpected.
*When I was a kid, I wanted to be an astronomer; can you say "NEEEEEEEEEEEEEEEERRRRRRRRRRRRRRRRD!!!"? But hey, nerds are OK and are sometimes cool. There, that's the extent of my olive branch. Take it or be swatted by it ;)
**Some other interesting Colliding Universes posts with article links can be found here, here, and here.