I don't think the review process matters because their plenty of apps that don't support voice over at all on ios. I think it comes down to apple supporting it much earlier and advocating for it. More blind people started using iOS and then support for apps started getting better.
A major difference (that the review process could influence) is that iOS apps seem to be pushed toward using native controls whenever possible (or abstraction libraries atop those controls), where Android tends to have a lot of custom controls. The native OS controls have very good accessibility, so the average iOS app (which leans heavily on native controls) should be more accessible than the average Android app (which doesn't.)
The differences probably come more from the splintered android landscape and Apple's stricter review process.
Source: met him