In my opinion its a gamble by Canonical. Patent royalty fees level the mobile and tablet playing field. Why would any hardware manufacturer use Unity/Ubuntu when they could either use Android from Google, or fork the code base like Amazon and the Chinese are doing. Likewise Microsoft will likely subsidize manufacturers to use their Metro OS, which Canonical cannot match.
A key is how to monetize content delivery and search results. I don't see what Unity/Ubuntu adds that iOS and Android don't already have
One thing Linux has is that it lets the user control and customize their system, and it lets an ecosystem develop where new system behavior can be created.
Not present on Android and certainly not on iOS.
But you probably don't value that if your concern is how to monetize content delivery.
A key is how to monetize content delivery and search results. I don't see what Unity/Ubuntu adds that iOS and Android don't already have