Curious about inconsistent DNS service

[MsOsWin at nonooo.com]

Today my ISP seems to have DNS trouble. (Recording on voice support 
simply says they have trouble. Unspecified). I discovered this trouble 
by checking log of batch pings, pinging domains or pinging true 
numerical IPs. 

(some of) My news and mail setups uses true IPs, so work fine. The true 
IP for my ISP's http works in the browser. But my ISP's domain name 
doesn't connect.

I've tried a few big-name links. Google. BBC, yahoo... no connect, and I 
see dnserror flash in status bar.
I've disconnected power modem, router, and shutdown computer, then 
reconnected, restarted. Seems the same. 


I expect the ISP will fix whatever they're working on, so no worries.
But I'm curious if there's a reason for this apparent anomaly: 
http://www.sfgate.com/ connects, navigable!

TIA, etc. :-)