Well Mogamer, I would have to say that you haven't seen that many HDTVs then. The standard is 3.5mm, because, quite simply, that's the connector at the other end (the one that jacks into your PC), hence the easiest solution. Mine may be LG, but I've got 3.5mm too. 2.5mm is like... iPods only. At least, here in the UK.
RCA doesn't sound too probable, simply because it would require an adapter.