They don't. The HOME-XXXX format, where XXXX might be the last 4 digits of the MAC address, is the default SSID for Comcast "gateway" style wireless routers. I'm not sure when this started, but my guess(tm) is about 2 years ago.
Anything is better than linksys, dlink, default, hpsetup, and default.
3.74% of about 210 million wireless networks use the default SSID. I guess this is proof that most computer users have no imagination.