Why does everyone need to run a full node?
No, not "everyone" has to run one. We're already pass that point IMO. However, you should be able to run a node without it costing you a lot of money (this is subjective I know) if you want any kind of decentralization.See section 8 of the bitcoin white paper. Even Satoshi viewed full node operation as a business activity. If you didn't sign up for Satoshi's vision, what exactly did you sign up for?
Just because Satoshi had a view regarding something, that doesn't mean that they were right. I disagree with 'running a full node to being a business activity'. It's not like the node count isn't slowly going down due to the ever increasing resource cost required to run one.Remember, BTC is now being ran by these types:
-snip-
So we should believe in Ver's words, the same person that vouched for Mt.Gox solvency? -snip-
Yeah, it is subjective. My desktop could easily handle 20 mb blocks, and it isn't anywhere near top of the line. Sure, in 5 years I'd need more disk space, but I could also buy enough disk for 20 years at that rate for less than $600. In 5 years when I actually need it, that storage will likely be even cheaper. The CPU, RAM, and network connectivity I have today can already handle it.