That's interesting. I guess Apple decided not to enable vsync? I don't recall seeing tearing playing games on my 4S though, can developers elect to turn it back on?
[1] I can only assume the new iPad's LCD is more inert in some way? Smaller pixels, slower crystal?
On the iPad, on the other hand, there are tons of horizontal lines in a table view, for example.
Also, I thought about the 60 Hz thing, and I think high frame rate is a bit of a red herring. After all, the lines actually are slanted; the higher the frame rate, the fewer degrees they're slanted at the same scroll speed, but whether we notice the slanting is independent of the frame rate.