I've been wondering too. My current theory is that it's spammers testing whether submission is unmoderated.
Is there a solution to this in the works?
EDIT: Are you worried about the server? If you make a spam filter algorithm, then this is more likely to increase the load on the server, which increases the latency... and as a result, increases the headache?
But if we assume that they will take HN at any cost, then their course of action will match that of bacteria: attack, mutate, rinse, repeat. Eventually it will be either them or us that survives. And it probably won't be us.