icloud iphoto library beta vs icloud backup

I don't understand these two services, what's the difference?

When I lost my iPhone back in 2012, I simply bough another iPhone, typed in my e-mail and everything from my lost phone was there after downloading, all my photo's, everything. I could also download iCloud for PC and all my photo's would sync to my computer. When I plug my iPhone in and it's connected to wi-fi, it uploads all my data, including photos, to icloud.

So what's different about icloud iphoto library beta?