At the moment all players are within the rules, but as tgg said earlier, it's not really within the spirit of the game.
Edit: Lets give it a little time. From next month the profiles will be open, so we can see who invested well and who is misusing the system. In any case, there's likely to be a fall from the top as quick as the rise to get there.
For next year there will have to be a filter to stop people from buying shares they generally could not, I'm still looking for a decent way to get those numbers. Is there a list somewhere of total monthly volume?