If the market were to drop significantly below 285, why wouldn't GE continue to accumulate shares? After all, it would be a bargain and a step toward full ownership should the blockers get tired.
The key point is that, as long as GE doesn't get 90%, the stock will remain publicly traded. GE may have enough ownership to exert significant control, but as long as that doesn't mean running the company into the toilet, which is hardly in their self-interest, it means that the rest of us can participate in future growth. Indeed, one might anticipate that, if GE cannot gain control, but they see Arcam as key in their future (which seems apparent), that we are likely to see a big order soon after.