It's the critical mass of friend's that key though. Hell, Paypal is just as effortless once that critical mass is hit, and that's has been around since 1998.
Paypal's UX has changed to be simpler, but I don't think they even had a mobile app for the longest time. It was also several inputs, such as choosing the type of transaction to make sure you don't get charged a fee for sending money to your friend.
I'm not going to go home and remember to paypal on my desktop when I could just use the venmo app to send you money right after you paid.
I'm not going to go home and remember to paypal on my desktop when I could just use the venmo app to send you money right after you paid.