I think there is more to Branson's ideas than he lets on.
I can't help but think most of the Virgin Group's Transport companies' profits being donated to the environmental cause involve a bit of creative accounting. As more and more environmental factors come to play in the economy so will the need for less environmentally damaging products and services. By investing in such products now and after making such a grand PR statement, he gets to make quite a mark, let alone allow himself to get a foot hold in the developing alternative fuels and technology sector, as well as the more environmentally aware consumer market.
Additionally most of the ideas he's supposedly coming up with to reduce fuel consumption (and hence also costs) are out there being developed already, e.g. the self tugging aircraft gear. I have suspicion that he's made some calculations, figured that he can meet his 'personal environment targets' using such devices and appeal to the growing environmentally aware market as though he's taking big initiatives to reduce his company's impact.
By being the first brand icon to publicly do this, he ends up with the most credit/identity in the eyes of Joe Public, and thereby most share of this developing market.
Let's be honest, if BA or BMI came out and said they were increasing fuel efficiency, Jo public would regard this as a way to reduce overheads rather than 'benefit the environment'.
I'd also be very interested to know how his Virgin Fuels investment unit works - is it a registered company or a charity?