That's worst case, and like I said, it's easy to check/recalibrate beam-type wrenches. I don't know why people would use anything else -- they're inexpensive and great for letting you know that you're approaching the target torque. The recommended torque values for bike parts usually have a generous range, so if you aim for the middle, you're likely to be just fine.

I like how people will cite the fact that a torque wrench can be slightly out of calibration for telling an absolute mechanical newbie that they don't need to use one.