There's a bug in iOS 8.0 with Voiceover in UIWebView. I've filed it on Apple's bug report site and also made a copy available on OpenRadar where you can read it.
Summary: Consider a UIViewController containing a UIWebView whose HTML content is long enough that it scrolls off the screen; at the bottom of the HTML is a button. Voiceover users can right-swipe through the content to have the text read aloud.
But when the Voiceover user swipes to the button and double-taps to activate the button, nothing happens; its onclick event handler never fires.
Is there a way to work around this bug? Or do our Voiceover users just have to wait around for Apple to fix this bug in a patch release to iOS 8?
The workaround is to switch to WKWebView. The bug exists in UIWebView, but not WKWebView.