Ok, I'm back.
Just cant help myself
As pointed out, Sprite's latest link was to an out of date document that is also out of context.
I have a new link to back up our side of the argument.
http://www.atsb.gov.au/publications/.../B20040246.pdf
See chapter 7.
The requirements for weather-based decisions on the carriage of extra fuel to fly from the destination to an alternate described earlier are only applicable for pre-flight planning purposes. Once an aircraft is flying, the rules for carrying fuel to meet weather-related alternate diversion requirements do not apply, as it is not normally possible to refuel in flight. Allowances for this risk exist in conservative rules that provide a margin at the planning stage to provide for some inaccuracy in a weather forecast. This risk may be further mitigated if a pilot monitors a destination’s weather information while en-route, and elects to divert in flight to another aerodrome if the destination’s weather deteriorates.
The ATSB is pretty damned clear on their interpretation.