[phjohnst]

Risk/reward.

If you got into China 15 years ago, you had no idea how things were going to pan out (and you deserve compensation for holding that risk). If you get in now, there's a more likely chance (I'd argue) that you'll do well, so the risk, and therefore the compensation you deserve, is lower. And holding currency is a lot less risky than equities, anyway.

The people that would be interested in a Yuan bank account up to $20000 aren't really sophisticated investors anyway.