As @BethBowers noted, they have made some paperless enhancements in v2015 for PO. But unfortunately, it still appears that the paperless e-mailing interface for the various modules (SO, PO, AR, etc) were written on opposite sides of the world and no one bothered to develop a common feature set for them. You can do things in SO that you can't in PO even though the need is there. I brought this to Deborah Nelson's attention during the VIP program. Perhaps v2016 will be better....