Well.....correct if I'm wrong, speaking in terms of computers...setting a high refresh rate is like overclocking your monitor, if it is designed to operate normally at 1024x768@85 hz, by setting it to 100hz you're OC your monitor

hyeah: , you're making the monitor do too much work. The reason is that the higher the refresh rate, the faster the electron guns have to switch between colors for adjacent pixels, so in layman terms, your electron gun inside the monitor is firing electrons faster.
So if your monitor is suppose to last 5 yrs @70-85hz, it'll last 3 yrs @100 hz.
Some more useful reading.....
Refresh Rates and Interlacing