e.g. no blend mode except "normal" really works reliably across browsers yet. And just a reminder: it's 2013, everyone.
But I agree with your argument regarding to something is not properly - yes, that can be the reason why people don't see the whole thing as reliable
Compared to what? What alternative does reliably have blend?
So the only alternative is something that's been pre-composited down to pixels for you, probably in a png.