When you add yourself to a bug's CC list, every other person CC'd on the bug is sent a "bugmail" notification that you are now CC'd. If you just vote for the bug, you can receive bugmail notification without spamming all the other CCs. That's what I do. :)
Yes, the CC list will subscribe you to email notifications about the bug, and does not really indicate support, only interest in receiving email notifications about the bug.