Capetonian,
I am heavily critical of hs2 too, but I don't accept your assessment. Old Oak Common is one of the better parts of the project, as it would allow easy cross-platform interchange onto Crossrail. Tunnelling through to Euston on the other hand, is exorbitantly expensive for relatively small gains, as you are still on the northern side of Zone1 - but I wouldn't call Euston, where services are currently planned to terminate - the 'outskirts'. It just isn't the best place either - and no consideration has been given about the need to rotate Euston if Boris Island goes ahead.
Also, it isn't about saving 20 mins to Birmingham - the time benefits are much more significant once it extends to Leeds & Manchester, and even more so to Scotland.
Having said that, the first bit does indeed just go to Birmingham, with a spur stopping short of Colwich where the Manchester and Stafford lines meet - so much for capacity!
I could go on, but there is a Jetblast thread on that topic.
With respect to this airport though, there is no provision for a central London terminus for a link from this airport as part of either the first or second phase - everything is hinged on Heathrow, which is going to get even busier with its improved links via Crossrail.