etrade HKG told me that you need a brokerage account.
you can also have an etrade savings account, but the funds are transfered into the brokerage account, then you can move them to the savings.
i just did the first transfer from HSBC HKG to Etrade yesterday. It took a while to set everything up (including adding Etrade as a 'registered account' with Etrade), but it worked, and was all free.
Etrade HKG actually wires the money to Etrade USA for you, once you transfer the money from your HSBC HKG account to their HSBC HKG account.