Legally, probably not. They aren't demanding that you not redistribute, just asking. And asking politely. They are banking on the good nature of people. Good for them! And us.
All our developers wanted to just post the source online and be done with it, but our boss had security concerns he wanted us to address first -- so in the meantime we gave people who needed it GPL'ed copies, and asked them politely not to redistribute until we were ready.