There's nothing inherently inaccurate about a belted cartridge.
However, most winning long range target shooters nowadays are not using belted cases. The current trend is toward shorter, fatter beltless cases. The theory is that shorter fatter powder columns offer more consistent ignition. You'll see lots of WSMs, SAUM, and a bunch of .284 based cases. The 1K bench rest guys seem to be in love with the 6 dasher.
Belted cases are avoided for several reasons...
First, when you size them properly (headspace them off the shoulder instead of the belt), standard sizing dies don't size the area just above the belt. With stout loads, brass will flow into this area and cause problems in a tight chamber after a few firings. Specialty dies can fix this problem, but it's extra expense and/or reloading steps.
Second, most belted cases are magnums and the recoil becomes an issue. BR guys don't want to upset their rifles on a quick string, F-Class guys don't want to take the pounding from a magnum case over 100 shots with a brake-less rifle. Ditto NRA Highpower competitors.
Third, most target guys want to start with the best brass money can buy, and the field is limited for belted cases. Lapua for example, does not make belted cases.
Again, I don't think belts make a case inaccurate but for the reasons above, the serious target guys have evolved away from using them.
-nosualc