Yes you right, both are good enough and everyone want to simplify his backend schemas...

I want to note big difference between haproxy and nginx, first of all "nginx is webserver" (nginx HTTP server) and then proxy/loadbalancer(may be used) whereas haproxy is pure loadbalancer. Enterprise bare metal and hardware appliances for proxy/loadbalance built on top of haproxy

nginx is wide spread because of usage as good minimalistic web server