I think the main reason for the tracks having to be dirt is really as that's what the cars were designed for, and how R/C racing started off so don't think it's a big issue really....
I don't know why we struggle so much to have dirt tracks, there's loads for 1/8th and most european countries all race on dirt so it's not all about the weather..... We had some great dirt tracks in the past
Anyway, no point worrying about it is there as Lee and Darren have proved, they can still mix it up and beat the best in the business and it's not the first time either, remember how well Lee's done over in the States at various Cactus classics and JConcepts meetings?