i have a 02 WRX 20mm rear bar w/ hardened links and the stock mounting bracket. no problems here (MY00 RS) for a few years..
There are a few companies that make the HD upraded brackets such as whiteline. There are reports of people that have broken the stock ones with larger bars 20+ mm bars which neccesitated the upgrade.
I am going to upgrade soon but to the 04 OEM WRX brackets.. they are cheaper. ~$40 vs. ~$100 and alittle sturdier.