Hi Mike,
I'm not sure who told you that you cannot upgrade an A2 TDi via the serial port but they are very wrong.
The only error stored on an ECU after disconnection is battery voltage too low. this causes no problems whatsover and is ignored by the ECU, it's just a log.
With Postal on ECU's many companies do this such as APR, GIAC, Revo, Abt etc with the same knowledge of the voltage too low log. You can clear the fault on the bench with a dummy loom handily.
With the A2 TDi OBD programming is totally possible, Milford Micros programmer which we use does this, the EPROM is a AM29F400 and it's EDC15P/EDC15P+, hardly a tough one to program, Many OBD tools can do this;
http://www.cmdtec.it/prod_BDM_OBD.asp
http://www.optican.net/
http://www.byteshooter.de
even kwp2000 will do some of these
If you doubt my expertise I my past employers include APR and AmD and I currently work with Oettinger and also am the lead moderator on the checksumm.com forum which is a forum for tuners.
I write my own software as opposed to Stealth which were getting theirs from Geoff(ex AmD now living in Canada(good friend of mine and an ex employer and teacher)) and CCC who are an upsolute reseller.
Am I treading on some toes here? If so I do apologise. I don't have a huge marketing budget or give anyone any commision just giving a genuine service and with a sound knowledge in this industry.
I've had more than five girlfriends in the past but it doesn't mean I understood them. There's a huge difference between basic modifying and understanding hex code. I do nothing else than working with software tuning in the UK and abroad with other tuners in performance and fuel consumption testing.
I'm not sure what comments of mine you are unhappy with apart from the A2 tdi not being flashable via OBD which it is.