It's pretty simple, apple doesn't want you to be able to stream tv or videos for free as that would hurt itunes movies and shows sales. Also they would not sell as many games because there are tons of free flash games. This is the main reason for not doing it because would you really buy shows if you could just use hulu for free. This whole excuse it kills the battery or takes up alot of memory is just crazy.
Anyway comcast might create an app that uses their xfinity site and that alone with be the best app ever for the ipad. It's like hulu but better no ads and you get to watch all the networks including hbo, showtime, cinemax, etc. Whatever you have at home pretty much.
It's so funny to hear people who really know nothing about the web talk about how html5 is better and flash will be history very soon. Ask any web designer if he thinks flash is going anywhere anytime soon. Apple will bring flash to the ipad when android picks up and people see their tablets running flash with no problem.