11/27/2014
Take a look at this article from Apple Support. http://support.apple.com/en-us/HT201686. You have to be able to upgrade your old machine to Yosemite (or whatever OS is on the new machine). Too bad for all of you who have machines that can only go to Mavericks. Interestingly enough you can't even trust a Time Machine backup made on a different model Mac running the same OS.
This article explains why you should not install a version of Mac OS X earlier than that which came with your Mac.