But as a content producer you're not burning stuff onto writable Blu-rays. You're pressing them in a factory at a cost well less than $1 a disc.

Whereas a USB stick, even bought in large volumes, can only be so cheap.

You don't care if memory sticks can grow - you have, say, 20GB of content you want to deliver to your customer. It's just extra cost if you buy a 40GB memory stick to carry it.

I just don't see any incentive (other than marketing/coolness) for distributing anything on a USB stick.