Two things.

1. People are confusing internal with integrated. The integrated headset uses the head tube itself as a bearing race while the internal has cups that are pressed into the interior of the head tube. The Zero Stack is an example of an internal headset. Frames built for internal HS's tend to feature more dramatic flaring of the head tube in order to accommodate both the bearings and the cups.

2. While I believe it to be a solution to a problem that doesn't exist, the real-world testing of internal/integrated headsets suggest that there's nothing to really be afraid of. There is a dizzying array of standards, though. Personally, I would steer clear, all else being equal. I wouldn't make it my sole purchasinge criteria though.

Then again, I only have one bike that even has a threadless headset and I'm about to sell that.