No matter how widespread HTML5 is going to be, there is always stuff that is going to be in Flash, and even if EVERYTHING is replaced by HTML5 or whatever, that hasn't happened and won't happen for a while (hence the "slowly being replaced by HTML5" part).
"We didn't include Flash on this because HTML5 is the future" is a bullstuff excuse on Apple's part.
And furthermore, does the iPad even support HTML5?