Why? Euro is the most liquid and volatile enough currency pair and one of the world's best instruments for day trading.
Thats when you will see the difference on your system between longer time frame and short time frame.If e/usd starts behaving like noisy pairs , the systems can fail.
I watch & trade EURUSD almost every day since 2005... As you probably guess, there were times it behaved very differently during these years, from pathetic chop & creep of 2007 to insane volatility of October 2008. Also traded a variety of other instruments. Same principles everywhere, provided there is enough liquidity and volatility.
Of course it doesn't mean use 6 ticks stop blindly for every instrument in the world. It should be adjusted and may vary from 2-3 ticks (FESX, FGBL) to 10-15 ticks (CL, HSI).
I like challenges, so checked GBP charts to see if my stuff would work there... Looks even better than Euro due to high volatility of the cable.