I think it's better stated
"The important thing is that Apple may mainstream the purchasing of video content legally"
As before the ITMS existed there were legal music sites you could purchase music from such eMusic, listen.com, etc. What Apple did was make it easier for the mainstream consumer to buy that one new U2 song they liked without having to buy the entire album and also easily transfer it to an external device. Apple of course had the marketing budget to sell the idea, while other vendors with lesser marketing budgets kept trying to extend the capabilities of thier players and gain market share.
Currently there are legal methods to get video content on to a wide variety of portable devices, but they aren't mainstream and probably being used by early adopters. Apple obviously has made it easy and will be able to market the service better than Cinemanow, etc.
The bigger question is how many more new iPods will Apple sell? Is there a pent up demand among people wanting to get video content that can be watched on two inch screen? How many current iPod users are going to want to spend the money to upgrade.
Personally I think it's great that Apple is trying to push Ondemand primetime programming, but I don't thing they revolutionize it...