I am not sure which accessories you mean...but if you talking about the batteries, do bear in mind that only Sony batteries are INFOlithium which give you the actual percentage of battery life on the screen all the time (not including a230/330/380).
If you compare flashgun prices, Sony is still the cheapest if you compare amongst the same specs.
If you compare lenses, I don't think other brands are cheap either.
If you compare handgrip, same as well...
So I dun really know what accessories you are comparing with...:dunno:
I fully agree. In fact, Sony lenses are frequently cheaper than the other brands (look at the Nikkor 24-70...) and yet we can even get autofocus Carl Zeiss optics!!