Although I haven't tested this in any meaningful way, I'd be willing to bet OnSwipe simply relies to heavily on JavaScript. My iPad 1 struggles with any page loaded up with scripts, even ones that seem like they might not have any at all. For instance, news websites are often chock full of scripts for analytics, social media plugins, and advertisements.

OnSwipe probably works pretty well on desktop machines where it's developed, but today's tablets simply can't handle the processing and memory requirements necessary to make it an enjoyable experience.