[ASnep]

Quick question. For this, I have an example point. (BBC2 HD) A nip around DigitalBitrate reveals that all of the BBC2 HD variants are broadcast in some form of AC-3 on satellite and cable. (BBC2 Wales HD and BBC2 NI HD are broadcast in 2.0 Stereo on satellite with BBC2 England/Scotland HD being in 5.1 Surround. I don't know about cable because all of the BBC2 HD variants are encrypted and DigitalBitrate doesn't specify a type of AC-3 for encrypted channels) A look for BBC2 HD on Freeview shows AAC Stereo.  Is there a technical issue preventing HD channels broadcasting AC-3 audio on Freeview?

I would be cautious about what DigitalBitrate shows in regard to surround sound. Broadcasters can change from Stereo to 5.1 and back on both AC3 and AAC (yes, AAC also can do 5.1). So for DB to show 5.1 the last snippet they recorded had to have been during a 5.1 broadcast. They used to have a chart showing Stereo or 5.1 for all recent samples they recorded (like they do for the bitrate), but they have removed that for some reason.

The last snippet they have from BBC 2 HD on satellite looks like it just so happened to be taken during a 5.1 broadcast. Movies do often carry 5.1 sound.

As for Freeview DVB-T2 can do AC3 (and E-AC3) just fine. And according to Ofcom's Reference Parameters (www.ofcom.org.uk ) both AAC and AC3 are permitted as "Alternative Audio Encoding" to MP2 audio (see section 2.19). So it basically just comes down to the preference of the broadcasters (or just preference of the BBC since they are responsible for the multiplex).

EDIT: Or the solution they choose for AD like Technologist mentioned.