The sticker is not saying that the stove does not need to be earthed. It is saying that the stove does not need to be protected by an earth-leakage circuit breaker.
simulate this circuit – Schematic created using CircuitLab
Figure 1. A domestic fuseboard layout - Irish style.
Due to the amount of steam and spillages produced in cookers and stoves the likelihood of earth leakage is quite high. If the stove was protected by an earth leakage circuit breaker (ELCB / RCD / GFCI) nuisance tripping would become a problem. Because the stove is a fixed installation and more likely to be installed professionally the assumption is that the earth connection will be good and protect the chassis from reaching dangerous potentials. Similar decisions can be made for water heating, etc.
The highest risk of electric shock comes from portable appliances where cable damage, DIY errors, and accidents such as cutting through the hedge-trimmer cable, etc., are common and so earth-leakage detection is applied to all power sockets.
Interestingly lighting circuits can also be exempted on the basis that the number of accidents resulting from people stumbling around in the dark trying to find the fuseboard would exceed the number of electrocutions from lighting circuits which tend to be well out of harms way.