Lie said above it is all a matter of scale, if you are the copyright/trademark holder it might be a good idea to get multiple TLDs but it isn't really necessary. Think of it more like a ploy by registrars to frighten people into spending more money than they really need to.
Only buy the .net and .org if you are afraid that someone might come along and steal your customers who are looking for you specifically but this doesn't generally happen for a long time until your name is universally known.
It may be a good idea to buy your country extension though, I know for England here .co.uk is a very strong one with over 70% of people recognizing it and typing it in before they go for the .com.
The trouble with buying every extension is that you will probably need to translate and it will get very, very expensive with some registrars charging up to and beyond $250 for some reason.