I may well co-drive a diesel powered beastie, but I do like hearing a good racing petrol engine on full noise as much as the next man or woman, but a lot of the change in direction is down to marketing and the environmental side of the house.  In our Off-Road Championship, aside from it being increasingly difficult to find good venues, the use of bio fuels is positively encouraged.  This year, the first 3-day BAJA GB was held succsessfully and the FIA have now sanctioned it as an international round from next year.  A quote from the organisers "Sustainability will be a priority for us in devising and arranging the event and, in particular, bio fuels, already being used by some UK competitors, will be encouraged.”   Much more difficult getting bio-petrol than bio-diesel, hence the popluarity of using diesel, although Nasamax did a fine job of using bio-ethanol from purely bio sources, rather than a 5% mix of something biological with 95% non-biological, which is what most of those running so called "bio-fuels" are doing.   Oh, and the UK government taxes bio-ethanol as alcohol, which makes it prety unviable economically on its own.   All a sign of the times methinks,
MG Mark