The only MAC address Blizz gets to see is the one that's attached to the last device communicating to them. This can never be your PC (unless you're hardwired into the Internet). It's usually your router or your ISP's connection.
no offense but this is actually wrong, blizzard could read the "Soft-MAC" from the registry and use it.
and they would also not see the MAC of the router or ISP because IP does not transmit MAC addresses, only ethernet transmits MAC addresses and ethernet is only used in the local network.
Blizzard bans no HWID's because you can also "change" it, I am not going to explain how, because my English is not good enough for.
Blizzard dont ban any IP's because very few people have a static ip address.
sometimes they ban pro*xy ip addresses, for obvious reasons.
if they ban an ip then only for a short period, and if in the period, a accout logins on the ip, the account is monitored immediate.
if you get banned it's most likely because of reports or to much uptime(unsure about the uptime because even i am sometimes botting for more then 24h)
i know my english is not very good, feel free to correct my mistakes
tl:dr:
Blizz dont use MAC or HWID to Bann accounts
~d0x