Yes, but some people have better things to do with their money. I wouldn't put 800k in a Thai bank account earning 1% interest when I've got a pension which easily covers the 65k requirement. I have to transfer funds anyway, so it's much easier to kill the two birds with the one stone.
It might need to be an ED visa from a university, not a 90-day language school version. It seems the banks are looking for something more "long-term", not just 90 days
You won't get a letter from immigration saying it's ok to open a bank account. All you'll get is a certificate of residency which does nothing but confirm your address. You take this to the bank, but the bank will still need your passport with non-immigrant visa and probably a 12-month lease before they'll open an account