Many organic compounds are ignitable, putting them in direct flame may cause fires or combustion. it is possible to start a fire on a hot plate, but typically hot plates are not heated as high and the temperature is somewhat controll-able... you can not control the temperature of a bunsen burner very easily i would not through acetone or ethanol on a hot plate, as it can catch on fire or cause burns, but it's much worse with the bunsen burner.
