True, Yoda...they don't have to be the same company. But considering that both ECost and PcMall/MacMall/IdeaMall are situated at the identical address, that does increase the odds that they are, just a bit 
IdeaMall, Inc.
2555 W. 190th Street
Torrance, CA 90504
eCOST.com
2555 W. 190th Street
Torrance, CA 90504
Edit: oops...now I'd say odds are 100% that PCMall.com, MacMall.com, eCOST.com, eLinux.com and ComputAbility.com are more than casually related: The Mall Family
IdeaMall, Inc.
2555 W. 190th Street
Torrance, CA 90504
eCOST.com
2555 W. 190th Street
Torrance, CA 90504
Edit: oops...now I'd say odds are 100% that PCMall.com, MacMall.com, eCOST.com, eLinux.com and ComputAbility.com are more than casually related: The Mall Family