Because all the options to PNH are rubbish. I would go through London if it offered an advantage. It doesn't. I have to stop over between 1 and 2 times. I can go through BKK on a number of carriers which is a bit hell-ish. I can go through HKG and gives me a day to stop in and see friends which is very pleasant though the MAN-HKG flight is a killer. I can go through Doha and SGN, which is easy, but the 787-8 is a killer. My comment on SE Asia should have been addressed as equally naff as from MAN. The comment for LHR about East Africa stands. BA removed their EBB flight, and their NBO flight is it a bad time to land in NBO. I can travel on the ME3 or ET (okay, via DUB or FRA) from MAN and have a much, much easier journey.
I think you mean that flying to PNH (Phnom Penh) is rubbish. South East Asia is generally well connected from Heathrow, with many direct flights often multiple times per day. BTW, you can fly directly from Heathrow to SGN (Ho Chi Minh) three times per week - no need to go via Doha. Otherwise, flying via Singapore looks like a good option - 5-6 flights per day from Heathrow or one from Manchester, and 4 per day from SIN to PNH.
To be honest, flying long haul is a killer however you do it. A fair amount of discomfort can't really be avoided. That's why I tend to go for the quickest option at the most convenient time, which for me is usually Heathrow both for the direct flights and the choice of times. As I said, I'm not great fan of the place but it's a "least worst" option in a lot of cases.
You can fly via FRA or DUB or wherever you like departing from London, with shorter average connecting times because the flights are more frequent. Of course, if you live closer to BHX or MAN etc and there are connections at a convenient time, that's a better option for you than Heathrow.
Yes, they are a killer. But you don't have to pay that, there are other options available.
True (there are other options between London and BHX), but they are slower and less frequent which makes BHX less competitive.
Doesn't take into account door-to-door times. The queues at LHR could easily pad out that 30 minutes, not to mention the traffic around London.
Heathrow's queues are a bit mythical - meaning they don't necessarily exist in reality, or at least no more than at other airports. My recent experience at MAN was much worse than anything I've seen at LHR for years (transfers excluded). British Airways advertise a 45 minute check in at T5 (
http://www.britishairways.com/en-gb...formation/london-heathrow-airport/heathrow-t5) and I can confirm that's easily possible if not really recommended.
You're right about traffic delays, but they affect Birmingham too. Even if we allow 2h for the advertised 90 minute journey (Google Maps makes it 1h05 right now, or 57 minutes without traffic - so that's being VERY cautious) the journey times from Oxford are the same, and the 20-30 minute bus frequency to LHR is hugely more convenient that a 2h frequency to BHX.
Personally, if I was going between Oxford and BHX, I think I would use the train unless there happened to be a coach at exactly the right time, and I wasn't in a hurry or travelling on business. That's why I'm a bit sceptical about this new bus service, regardless of the merits of BHX - the journey time is very long and the frequency is quite poor. Still, good luck to it.