People defend for Zeng because of two things:
1) The so called 'fraud' was supported by the government then, and he was caught after the government leader was changed and his assert was grabbed by the government without giving a chance for him to pay back the investors.
2) Just after the death penalty was approved, the execution was done quickly before notifying his family.
They are not saying Zeng is innocent and the death penalty is completely unfair.

There're also two things to clarify:
1) He indeed caused people to lose billions of CNY, and was not innocent at all.
2) His death penalty was debated for years online and finally approved by the Supreme Court, and his daughter knew that before he was executed. She just did not get notified the exact day of the execution and did not get her chance to see his father for the last chance. It was not a secret execution imagined by many westerners.

Let's come back to the topic. If BTCChina suddenly disappears with billions of CNY from the traders, then yes, they deserve death penalty. If they allow people to launder millions of illegal income or help people to transfer millions of CNY to overseas (to avoid this, BTCChina has daily BTC withdraw limit of 10BTC for unverified users), they maybe jailed for many years. But if they are forced to close by the government just because BTC trading is not supported, they will at most be charged on taxing and license issues.