What you are seeing is platform-specific behavior, a difference between BSD-based systems including OS X and other systems including Linux.  The difference is that the former systems support the DSUSP (suspend on reading input) terminal character in addition to the normal SUSP (suspend immediately) terminal character.  The default value for DSUSP is CTRL-Y which you can see in the output of stty(1):

$ stty -a
[..]
cchars: discard = ^O; dsusp = ^Y; eof = ^D; eol = <undef>;
	eol2 = <undef>; erase = ^?; intr = ^C; kill = ^U; lnext = ^V;
	min = 1; quit = ^\; reprint = ^R; start = ^Q; status = ^T;
	stop = ^S; susp = ^Z; time = 0; werase = ^W;

You should see the same CTRL-Y suspend behavior with other utilities reading from standard input, like cat(1), unless they handle that signal.  You can modify the behavior of CTRL-Y by disabling the DSUSP character, for example:

$ stty dsusp undef

See the OS X stty(1) man page and other references like:
http://www.gnu.org/software/libc/manual/html_node/Signal-Characters.html