I think you're misunderstanding or reading into false information being passed around on the forums. Your Sony Internet TV and PS3, as of this moment, are not platforms that have been made compatible with your Slingbox. It's not Sony that's doing the blocking....it's just that sling hasn't yet included either product as a connected device up to this point. Just because a piece of hardware has a browser on it, doesn't mean it's available to work with the Slingbox.
At this time, there are only three platforms, called connected devices, that work with the Slingbox. Boxee, WDTV live and Google TV and 4 if you want to include the defunct slingcatcher. Google TV doesn't need to download any slingplayer app. It's included with the Operating system that's part the hardware capable of running Google TV. The problem is that these connected devices have various bug problems and are not ready for prime time, which I think is the reason why slingmedia hasn't expanded onto further platforms yet, like the PS3. They are probably trying to fix bugs in the connected devices available before moving on to other hardware.
As of now, you've only got so many options. Wait until sling supports your PS3 or Sony Internet TV, which could take a while. Purchase a connected device, like the WDTV live streamer or Boxee hardware or buy Sony's NSZ-GS7 box, Vizio's co-star or a refurbished Logitech Revue all with Google TV on them. Outside of the Slingcatcher, which does work great, you could still buy a connected device and unfortunately still have issues due to the bugs, so the bottom line is there is no way to trick your Sony TV or PS3 into running Sling's webplayer through the browser until Slingmedia actually.makes it compatible.