They unify the way you deal with mouse, touch, stylus and potentially other pointing devices. While this can mean that developers using only one of those in a single application still have less to remember, it's mostly meant for actuall being able to write applications that support both touch and mouse, for example. For Microsoft, with a device that supports all three modes of pointer interaction, it's actually quite important if it's even possible (remember, you can write Windows 8 apps with HTML, too – and no one's going to be happy if your UI stops working with a finger or stylus just because the developer forgot to replicate the logic three times).

If you only deal with touch input then pointer events isn't more complicated than touch events, but with the added bonus that things work as expected with a mouse or stylus, too (except multi-touch, of course). Apple in this respect doesn't really need to care, because no one uses iOS with another pointing device than a finger (or a capacitive stylus, which, from a software standpoint, is just a thinner finger).