The worst case error on a resonator is usually around 0.7%, usually much better.
Not that it matters much for this discussion but the resonator on my UNO is almost 2% too slow. I can actually tune the internal oscillator to be more accurate (just less than 0.2%).
Strange... Maybe they should consider getting a better resonator. The parts I found on digikey were spec'd between 0.5% and 1% maximum error.
0.7% should allow for a change of 7000 PPM. Although this is quite a bit, it really only matters for precise timing applications of frequency generation.