Canadian sigs were only introduced in March 2011, so no one was able to put 40k down before then. Even if one upgraded from signature at that point they didn't have to send Tesla any additional funds....
I really hope they don't make us wait ~3 months simply to "reward" sigs...
No, they're not going to go out of their way to make you wait. From what I've heard they plan to start the R's very soon after shipping the Sigs.