Just a few clarifications:
SCT ERC is part of the ATA Standards, as I believe since ATA-6. Drives that "say" they support some ATA standard should support erc, but they may indicate differently. The ATA-8-ACS states that ERC-settings shall be volatile over Power-On-Reset of the device, meaning: once you cut power to the drive, the setting gets lost. If you reboot the computer where the drive is housed in, it depends on the behaviour of board and controller. If they just issue a soft reset, the setting shall prevail. If they cut power upon reset, the setting gets lost.
HD203WI are good drives, supporting ERC well. But in fact I came over this thread searching for a way to make the setting non-volatile. Which obviously does not exist, yet.
To turn on ERC, you'll have to send an ATA-command to the drive:
SMART WRITE LOG, Log Page 0xe0 (command log), the log page needs to contain the correct setting according to ATA-8-ACS
You'll have to send one command for each: read and write ERC timeout. I've implemented this successfully, meaning the drives report the settings I gave them afterwards. But I'm sorry I can't leak the code unless my lunch is paid for the next 10 years or so.
Notes on WD: (WD10EADS, WD15EADS, WD20EADS): the first versions (Nov. 09) with disabled TLER were badly firmware-coded. They indicated to support ERC settings, but always reportet "command aborted" - that way behaving very very very badly. The follow-up firmware just reports no support for SCT-ERC, which is the right way to go (if you get on that trail anyhow...).
Hope that helps understanding it a bit,
P.S.: for 3ware 9650SE and 9690SA we setup the drives to have 7s/12s. That way it's not too slow on reading and not too aggressive on writing to bad sectors.