I don't think we could hit 8000 sprites anyway, as I think c2's sprites have a lot more overhead than theirs do in that vid (c2's sprites have variables, behaviors, etc). They might even be using some sort of quick blitting technique I've heard people talk about, keeping the image locations in an array or algorithm or some such then drawing an instance at each location instead of having a fully fledged object at each location, which would result in no extra overhead at all per instance.
I did a test to find out how many invisible sprites with bullet and wrap behaviors I could get in a layout at 55fps:
Ipad 3, safari: 1711, cjs: 770
Iphone 4s, safari: 2197, cjs: 642
So it seems even with rendering entirely off it wouldn't get anywhere near that high. Although I suppose they could have that test running on some crazy cutting edge mobile hardware, but I don't think something like an iPhone 5 could manage it.