It's probably a balance. One of the most desirable traits of a convenience service like Redbox is the ubiquity of their kiosks. If every block had a kiosk run by a different service, it would be bad for the consumer because it would be difficult to know who to trust.
Yes, because it practically eliminates the competition in the market. Considering that Redbox recently raised their prices, the purchase of Blockbuster Express may have primarily been intended to ensure that BBX couldn't undercut them.
They have a monopoly on dvd kiosks but streaming is still an alternative.
Redbox has all the new releases, streaming never does (at least not under the monthly all you can eat).
I've never tried it, but www.vudu.com seems to have most new releases.