The thing with diabetes testers is that they are CHEAP to acquire - in many cases free, or damned near free. The cost is for the test strips - also not a major expense for most users or providers.
The thing with INR testers is that the machines ARE expensive, and not everyone is capable of doing a self-test (supposedly). Although testing is done, at most, once a week (and often less frequently), per-test costs are certainly more than diabetes testing. What the insurers don't understand is that the cost of a lab test is quite a bit more than self-testing supplies. Over the course of a year or more of testing, these short-sighted insurers will wind up saving money supporting self testers, instead of paying labs for similar services. (Of course, the lab test is still supposed to be the gold standard for INR testing, and self-testing still hasn't earned enough respect. OTOH - self testing doesn't always correlate well to the lab results). What the insurers also don't understand is the reduced risk of bad events if a self-tester can test weekly, possibly detecting anticoagulation issues before they become problems, versus the cost of missed issues that result from infrequent lab testing.
I bought my ProTime meters (I have an extra - if you're interested, send me a message), and an InRatio meter on eBay and have no complaints. I saved a lot of money buying them this way, and have been able to monitor my INR weekly (or slightly less often), so that I am usually in range. The only time I had a serious problem was when I was running low on strips and didn't test often enough.
As does Dan, I don't understand why insurers won't support INR self-testing for their insureds who are under 65 but taking warfarin. Even if calculated over a year or so, the insurers can be saving money, and if any of the patients avoid stroke or hemorrhagic problems because of lab tests done too infrequently, the cost savings would be much, much more than paying for a meter and weekly test. (Also - one factor nobody mentions is that, if everyone taking Warfarin had a meter or his or her own, the quantity of meters may introduce economies of scale for meter and strips and make it much more affordable for everyone - including the insurance carriers. The volumes will never match those for blood glucose monitors, but may be enough to make it possible to greatly broaden the number of INR self-testers).
Some doctors may argue that letting the patient do self testing takes the management away from them. This isn't so -- the warfarin is still available only by prescription. The doctors or clinics could require reporting, and recording of results, before prescribing refills, and the doctor or clinic can get as involved as it wishes with the management of dosing.