In zsh, the shell where < file1 > file2 works, the shell does invoke cat.
For a command line that consists only of redirections and no command nor assignments, zsh invokes $NULLCMD (cat by default) unless the only redirection is a < one in which case $READNULLCMD (pager by default) is invoked instead. (that's unless zsh is in sh or csh emulation in which case it behaves like the shells it emulates).
So:
< file1 > file2
is actually the same as
cat < file1 > file2
and
< file1
is the same as
pager < file1
