The reason to use more than one is to aggregate signals to take advantage of the fractal nature of price/time (otherwise you suffer from a narrow parameter set, i.e. you better pick the right parameter) and exploit hysteresis...But it still doesn't make sense why if you thought a MA has some effect to smooth out volatility OR as a trend channel why not just use one? To me its like having a chart with 3 indicators in the false sense that more is better, in effect what you will end up doing is having to wait LONGER for all indicators to give a signal in the false sense that that is confirmation. But there is no such thing as confirmation.
I don't know why you keep harping on about 'confirmation'. You're the only one who's even mentioned it.
Dunno if you've ever been to Jez Liberty's blog but he tracks simple automated trend following systems. Which have largely been flat/poor this year, but performed quite strongly last month. He's also taken the concept you deride to it's maximum and created a composite trend following index from all the systems.
Down the bottom is a link showing the systems (which include a few MA cross systems) going back 20 years across a basket of futs. YTD return for 10-20MA system is 17% and 10-20-50MA system is 26%. YTD for the 50-200MA system is -9%, for the 20-50-200 its 6.8%. Across a basket of over 50 instruments. I guess they must all be in a bull market....