Huh? Your saying HTML 5 and AIR aren't coming to PS3 because Sony aren't going to develop them?
Why do you think developing case-by-case apps is goingto be such a chore? Firstly each title would need to be created by the media company, not Sony. That is, the BBC creating PS3's iPlayer app, ABC creating their iViewer, etc. That's no cost to Sony. Secondly, a well designed system will take the standard media streaming tech unfiform across all these players, and the same interface resources, and just require someone to sit down with an editor for a couple of days to piece it all together. this would all depend on the quality of a Sony middleware solution, but it's certainly feasible and I think you are overblowing the cost issue. Yes, it would be more to the media companies than just using the same browser/AIR app that they've already written, but it'd be a negligable cost.
...as insignificant as porting a cross-platform media portal to PS3 through a specially designed easy-conversion process...Again, you're asking Sony to spend money to allow something that doesn't net them money! The cost/return balance is then completely against this. Whatever they can make money from, they can make money from through their own prorietary PS3 player, and the value proposition wouldn't be particularly affected against the competition. The games and media console can be left as a games and media console, with a choice range of Sony approved services like Qriocity which they make money from, and everyone wanting completely open platforms will need to get a net TV or PC or mobile - they aren't direct competition for the games machine.