The iPad graphics subsystem absolutely destroys anything around when the OpenGL spec was released and many of these screen-savers were designed against hardware that's unbelievably slow compared to an iPad.
He's not making a game that's going to drain the battery in ten seconds flat, he's porting screensavers made in the late 1990s that were never heavy-duty to start with.
Sure. But OpenGL ES was not designed for the iPad. The decision to reject immediate mode was made in 2003, for the mobile devices of that time. And it is used in the industry for devices much less powerful than the iPad, even today.
It continues to be a popular choice for anything like the iPad, where there is no legacy software based on regular OpenGL, because it is a much cleaner and much easier to implement stack, and because if you are writing new software you should never be using all of that old deprecated cruft anyways.
He's not making a game that's going to drain the battery in ten seconds flat, he's porting screensavers made in the late 1990s that were never heavy-duty to start with.