Clay:
Your assumption that these medical professionals have studied anticoagulation for years, or that they're keeping up to date on anticoagulation management is just not correct. I don't mean to scare anyone -- but the research I've seen -- written by doctors and researchers who have ACTUALLY STUDIED anticoagulation management and risk assessment -- state that it isn't safe to be below range for more than a week. No, there is no need to test twice a week. No, there's no reason to fear warfarin. No, having an INR under 2.0 for a few days won't make you stroke out. But there are solid reasons for testing every week (I've occasionally gone 10 days to 2 weeks -- it's when I went 2 weeks, with an INR that was reportedly in range, but wasn't, that this lapse bit me).
It is worthwhile to respect Warfarin, and to acknowledge that it is probably necessary to stay in range (or, realistically, above the bottom of your range) so that you reduce the risks that are associated with your INR getting too low. And, yes, if your habits, diet, and dosing are consistent, there's a strong possibility that your INR will STAY in range from month to month.
HOWEVER - for the six bucks a week that it costs to self-test, for me it makes sense to test weekly, so that I can be certain that my INR is in range from week to week, and to be certain that for some reason my INR hasn't somehow slipped out of range.
The fiction that studying medicine, or studying pharmacy, or reading journals means that these pharmacists or doctors are really up to date on anticoagulation management can be a dangerous one that too many of us are more than willing to risk our lives believing.
BUT - I know that I probably can't convince those who don't want to believe in the importance of weekly self-testing -- even if it's low cost insurance against an unwanted outcome. So, I'll see if I can kick myself the next time I'm challenged to respond to this kind of stuff.
(And, again, I'm not trying to scare anyone about warfarin -- millions of people take it -- with adequate monitoring and management, many of us are still leading productive, healthy lives)