That would be like saying Gold is a Ponzi scheme as well.

Nope, I click sell/buy, and directly after I get confirmation that I've bought/sold at x price and if bought, the coins in my exchange few days later, or if sold, the $ in my bank few days later :thumbsup

You still need open orders (from others) to be able to fill your buy or sell request.

If the "current" BTC price is $500 then there's no way you'd be able to offload (say) 100 BTC at $500 each...

True but my exchange limits me to 50 per day, and every time all my orders have been full-fulled whether I'm buying or selling :thumbsup