[jude-]

> this problem can be completely avoided if every method has no more than one external call and always puts it last.

Actually, it's a bit more nuanced than that. If you have methods that make external calls--even if it's the last thing they do--you still have to ensure that all your externally-callable methods do not share state with the methods that make external calls. Restricting where and how often you do your external calls isn't sufficient, since that last external call at the end of your method can turn around and call other methods in your contract (which can alter the contract's state, if you're not careful).

EDIT: clarification