I think, in general, people using Rails prefer to have all their code
within their Rails app rather than use stored procedures.
I use stored procs all the time with Rails, because I prefer to have
the database "protect itself" from bad data, rather than rely on the
application/s to do it for me. That's the big issue for me, although
I also use stored procs with Rails for other purposes.
It seems to be as much individual preference, and different
experiences, as anything else - I don't believe either approach is
"better" than the other.