CMC and Open Markets are CFD trading platforms - where you can...

CMC and Open Markets are CFD trading platforms - where you can leverage funds:
Eg. You have $1k they will enable you (for a fee) to purchase $50k worth of stock - if your stock goes up you make the $$ on what you leveraged, however if it goes down it will typically sell once you $1k is gone, or potentially it may not sell and you can end up owing a lot more than the $1k you lost.

This is likely why the number of shares traded on these platforms are typically high and the selling is in pips.