How one determines spam is important, but I believe that a technique known as "sliding" is occurring here. Spam is obviously one way to slide a topic off into the black hole down on page 99, but off-topic comments may be even better, as they seem to relate just because it comes up in the thread.

Consider if I had just now gotten involved with this thread. Unless I made my post after just reading the thread's opening post, I would have given up after less than three pages. Maybe what is happening isn't technically spam; but it is sliding the topic into oblivion just like spam would if unchecked.