Another thing to consider about market cap is that blockchain technology enables a bunch of other things that traditional media does not. User accounts with reputation (which has value in itself), being able to follow/reward individual content creators, not being tied to a single publishing house.
On the other hand some costs of having a public blockchain include the inability for steem-holders to profit from data mining user's data (since it's public and everyone can data mine it), publishing and curation tools are still in their infancy (for those who want to publish a controlled message), and the ability to publish with a centralized like model (still desirable as many many people are accustomed to the format).
Great response. I feel there will be many different chains along a spectrum of user permissions and oversight.