There are three main problems with all these discussions.
1. Exchange Rated purchases are based on the market leader pricing, right now that id GOX, so if I buy a product on amazon, it the BTC goes through a proxy that bases its price on GOX. This would not be a problem if the rate was stable. All the evangelists love to say they are in it for the love, but if I posted my wildcard SSL certs at 3 BTC a month ago, that was a good price, but yesterday that would be outrageous, so prices for real goods need to be exchange rated. Vendors choose the easiest to do business with. MTGOX was that. Somewhere someone needs to agree on what a fair prices is.

2. Single systems can survive DDOS, enormous scale demands, hack attempts and natural disaster. DNS and other rarely changing content is actually the most immune from attack if done right with BGP anycast. Anycast lets you have the same IP in multiple places around the world, hundreds or thousands of networks can have the same IP if the content is the same (or different if you dont care). Actually you could have anycasted servers pushing dynamic content on a proxied back end that only proxies the authenticated users and the back end could be completely hidden secure backbone. Not only that, major backbone providers have a mechanism for blocking attackers by pushing a blackhole route through bgp. And that is just the stuff from 15 years ago. I am sure the new stuff is better. This is the stuff that cloudflare kind of offers as a service with public back end.

3. Craigslist is the perfect decentralized exchange. How do you upload USD to the Internet? Meet me at the coffee shop, hand me cash. I send you BTC, drink a latte while you wait for some confirmations, but I base my price on.... the leading exchange. ARG we keep going in circles.