alright, never mind what I said before:

http://tldp.org/LDP/abs/html/process-sub.html

Looks like the equivalent of the "read" example partway down the page. curl is actually being executed in a subshell.

using only the second "<" would result in bash being called with a argument like "/dev/fd/N", which is where the output of the subshell is coming from.

The first "<" redirects the output of this file descriptor into the stdin of bash.

So both are needed, but you could just do it with a pipe :/