Here you go:
http://computer.howstuffworks.com/offset-printing2.htm. You need to make a new plate every time you need to correct an 'a' to an 'e'.
Here's a fun fact. According to an article published in
Nature, even Britannica Encyclopedia has an average of 2.9 errors per article. But you just trust it is correct and is the gold standard because you don't know better. If FA never published their errata, chances are you'd think what it says is
the absolute truth too.
EDIT: Also, about you saying them taking $50 for embryology change, get this:
no one is forcing you to buy the newest edition! Them changing the layout of their book is their decision. Heck, if you are happy with 2009 edition, you are still welcome to use it. They are not going to take back your old book because it is now 2013.