If you haven't read it already, check out Scott McCloud's Making Comics. The entire book is fantastic, and in particular the section where he talks about visual techniques in manga, and how Tezuka invented most of them.
The impression I get is that people are surprised since they're not used to it. But it's not incomprehensible or difficult to understand once you do, which makes it seem more like a different convention than a real cultural difference.Really? I see it complained about all the time on here, or I remember seeing it when people talked about anime.