PayPal probably has good enough fraud detection that easier-but-riskier integration is still a net win for PayPal. (Not so much for the rest of the internet, though...)

Similarly, Google's "No CAPTCHA" (https://news.ycombinator.com/item?id=8693767) lets Google offer a better experience than a traditional CAPTHCA. I'm somewhat surprised that better fraud detection leads to better UX, but it's pretty neat.