No, you don't need every TLD. It's this kind of mentality that has blocked off so
many domains, and necessitates new tlds. I would say from a business perspective,
if you want to be safe, get .com, .info and maybe .biz (in case corporations switch
over to them, but I doubt it). I don't think you need a .net if you have a .com (unless
you're business is relevant to the internet infrastructure). You certainly don't
need a .org because if you're a company, no one will try that address before trying
.com, .biz or .info.
If you're non profit, I would go for .org and .info. Possibly
.com (I hate to say it because it is WRONG)- but only because of ignorance in internet
newcomers who think everything ends in .com who may otherwise not find your site,
and I would point it to the .org and have .org displayed clearly so they learn. Really
non-profit orgs should not have .coms at all. It is improper, incorrect, UGLY and
ANNOYING but unfortunately because so many already do, you might be at a disadvantage
by not doing. There should be no question whatsoever of having a .biz. That is 'at
one with the ridiculous'.