The idea of transferring tokens only when you want to sell them is a nice idea, but it doesn't work in practice for a lot of people. Imagine speculating in 30 different alt coins. It is just too much work to run wallets for each coin. So people keep them in an exchange. Also, people may want a lot of open orders. Successful investors can accumulate a lot of value in an exchange quickly.
0x doesn't solve the alt-coin problem but encouraging people to hold their own ethereum tokens is a start.
The idea of transferring tokens only when you want to sell them is a nice idea, but it doesn't work in practice for a lot of people. Imagine speculating in 30 different alt coins. It is just too much work to run wallets for each coin. So people keep them in an exchange. Also, people may want a lot of open orders. Successful investors can accumulate a lot of value in an exchange quickly.
0x doesn't solve the alt-coin problem but encouraging people to hold their own ethereum tokens is a start.