Well yes and no. The important thing is that the laser level accuracy is enough for the job that you are using it for.
In reality pretty much all lasers on the market today have a tolerance rated between 1mm to 8mm in 20m. For indoor work over short ranges any rating in this band would be fine as most of the time you would not be able to or need to work to any better tolerances.
For long range outdoor lasers something within the band of 1mm to 4mm in 20m would be fine as users are likely to generate more error variance by the way receivers and staffs are used than by the tolerance of the laser itself. In specialised high accuracy engineering environment the tolerance of a laser becomes far more important.
The next points to cover; are the tolerance rating itself and whether the rating quoted has been checked post manufacture in the country of distribution. Many high quality brands will calibrate each and every laser level they sell and then put a calibration certificate with date on the unit, whether the laser maintains this accuracy depends on the quality of manufacture and how it is used and stored by the user. Also some brands will calibrated their lasers well within their quoted tolerances allowing some margin for change and still remain within tolerance. Cheaper models may well rely on the factory calibration before shipping and may also select a rating based more on marketing edge rather than reality this I would suggest is quite prevalent on internet auction sites.