All valid points......
Apart from the one about Vega....
Yes the XXX4 has been discontinued but still definitely able to get parts much easier than the XX4. Its one of those things really, and if you look at racing numbers and entries to large events, but also club racers, due to the fact the most club racers see 4WD as a huge expense, they go to Shourt Course trucks and 2WD in general. It is slowing, it is much quieter on club level, Horizon and Losi make no money from hardcore racers.... The money is made from bashers and club racers, they dictate where the company places all its eggs.
If you look into this, especially the US and Asia where the only money is made by these companies, you will notice this trend away from 4WD.