I don't know about 'everyone,' but I don't use a service. I know that **** reported that he had a service, but that it was hard to use and way too expensive, and as far as I know, he is self-testing and may also be self-managing.
It's been written that many (all?) of these services charge way more than is necessary, and that they're a rip-off of the insurer or government funds.
Personally, I've been self-managing for five+ years. I started managing once I was able to get a meter.
I personally do not trust my INR to the InRatio meters -- they report values that are significantly higher than the labs (or most of my other meters), and I had an 'event' two years ago that can be related to incorrect results. Plus, with the current supply problems and recall of InRatio strips, I don't know how affordable or available supplies for this meter will be for some time to come.
One of the more rational things about these services is that they seem to want weekly reports, which they call in to your doctor. Weekly reporting is good -- I often test weekly, and hardly ever go more than 10 days or so between tests. In spite of my being nearly always (with very rare exceptions) in range, I still want to test weekly (and usually never test every other week).
I have bought my meters on eBay. My supplies often come from eBay, although I've also used medical supply companies or other sources for the testing supplies.
You can often get a working meter relatively inexpensively on eBay -- just keep watching. Although the rules of this forum may require suggestions of only using professional sources of meters and supplies, I'm just stating what I've been able to do. In my experience, I've saved a lot of money buying meters on eBay, and have rarely run into problems. The InRatio 2 that Alere sent to me (after I reported a major problem resulting from probable errors produced by the InRatio 'classic') was one of the meters that significantly overstated my INR in many cases.
No -- you don't need a service.
I have a clinic that feels as if it is managing my INR, but with monthly tests, it really isn't doing me much of a service (other than prescribing my Warfarin and letting me get monthly blood draws that I compare to my Coag-Sense and CoaguChek XS (or XS Plus).
There are resources available (plus some of us on the forum) that may be able to help you do self-management. (I don't always trust the clinics or other 'professionals' to give good advice about dosing. I've ignored bad advice from one clinic, and am almost ALWAYS in range -- because I am able to self-manage). Self-management shouldn't be all that intimidating -- and, after all, it's YOUR life, and you have a much higher stake in keeping your INR in range than any clinic or service does.