You're missing the point. Yes, these things have meaning because we deem them to, which is exactly why we have to be discriminatory in what we give meaning. If everything is equally meaningful, then nothing is meaningful.
Something having meaning at all doesn't make it art. A log in the forest has meaning in that we can recognize it as a log and what relationships such an object can have with the rest of the world. This "sculpture" has that degree and type of meaning. It does not necessarily have the particular relationship that would qualify it as art.
Art is supposed to convey a profoundly empathetic message from the artist on an existential level that teaches the audience something about themselves, and by extension, the human reality. Simply seeing a log, as you would anywhere else in the world, does not carry the potential for that kind of meaningful social/emotional engagement.
Subjectivism in one's interpretation of such a message is not the same as subjectivism in regard to whether that message actually exists. Everyone can attribute their own meanings to things, but only the artist can engage his audience with a particular experience, thus making his work "art".
Sorry, I can't figure out how to properly reply to posts... BUT!
I disagree.
Your view of art seems a bit romantic. "Art is supposed to convey a profoundly empathetic message from the artist on an existential level that teaches the audience something about themselves, and by extension, the human reality." If this is true, than something like the Mona Lisa (I hate using this damned painting as a means to prove anything, but it works) is not worthy of the title of "Art". Indeed, it was meant to be a simple portrait of a woman. There was no Special Meaning, nor was there was some Great Truth encoded within it. It was just a picture DaVinci painted to put food on his table. The fact that the haunting face of Mona Lisa drew a reaction out of him and others was merely incidental. And yet, it did.
You posit that the artist MUST have some greater message to convey in his or her art, and that this message MUST be prevalent and remain the driving force behind the work. But what of art that is meant to invoke a visceral reaction? What about art that draws out an emotion, instead of a profound psychological truth? What about art that tells a story for the sake of storytelling? Or art that exists simply because it can?
What about art that conveys no message at all, except the one given to it by its audience?
If you're truly concerned about prevalent messaging, then don't these wooden logs, stacked by the artist responsible, convey an interesting one? Already, a forum thread with over one hundred and fifty posts debates over the validity of the concept. I'd call that a success, then: it has challenged your perception of art. Was it successful? Perhaps, perhaps not. But then, does it have to be?