Absolutely not true---KUSI and KSWB are also legally must carry stations in SD, and for competitive reasons XETV and maybe a few more Mexican stations are "virtual must carry" as well.
Yes, KUSI and KSWB are in there too. XETV does NOT have to be carried, but is, as you suggest, competitive reasons.
It's all going to be moot as the 'net casts a wider throw over the population and local tv stations will become obsolete. Newscasts will be on-demand and programming just an IP switch away. I would have read that in the paper -- but who in the frack buys them anymore?