A few observations:
1. It is not illegal, at least at the moment, to hold, send or receive bitcoin anywhere, including Russia and China. Holding, sending and receiving bitcoin is all the blockchain.info app lets you do.
2. It might be illegal in some countries (like Russia or China) to buy certain things with bitcoin or to exchange bitcoin for fiat currencies, however the blockchain app does not allow users to do those things.
3. Although it is certainly illegal (even in the U.S.) to do certain things with bitcoin (like buying drugs or guns, or laundering money), please note that it is equally illegal to do those things with the paypal app, or with your banking app.
4. You can still use Blockchain.info with your iPhone, through their mobile web interface. However, you will have to trust them with an online wallet.
5. Blockchain is pretty serious about security. I would trust Blockchain's online wallet over some of the offline android wallets that I have seen.
Just my two cents.