I would be in favor of downloadable content if the quality was there, but it just plain isn't. All of Apple's "HD" content maxes out at 720p and is highly compressed... it can't hold a candle to Blu-ray. And with these new higher-resolution screens in the 27" model, the video has to be upscaled even further.
Also, the other poster was right; even if the downloadable content was made available at 1080p and at reasonable bitrates, where do you think you're gonna put it? A dual-layer Blu-ray disc (the common format for commercial releases) is 50GB... that means you can put a whopping 10 movies on that 500GB drive (assuming you don't need an operating system). Let's be realistic.
These new updates (27" screen, 16:9 aspect, i7, 16GB of RAM) are all fantastic improvements and have made this new release worthy of being called a "major update," but the lack of Blu-ray capability is a glaring omission that shouldn't be ignored. People are right to call them out on it.
At the very least, consider this... the new Final Cut Studio has Blu-ray burning support built-in and I've been making discs with an external 3rd party drive for almost a year now. Seems silly, then, that Apple's own software supports making Blu-ray content but I can't watch it back on the same machine it was created with? Just nonsense...