Nikon and Canon are the big two. Sony is not that bad (in terms of third party accessories) compared to other brands. If I were the manufacturer, I would of course target where the market is.
Personally, I use Elinchrom Skyport trigger most often. Since there's no TTL, I usually carry a light meter in my camera bag.
Since late September 2012, Sony introduced Multi Interface Shoe (MI Shoe), which incorportes the standard ISO 518 hotshoe. I hope some third party manufacturers will make TTL triggers for Sony.
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