We also shouldn't forget the huge basic infrastructure that bitcoin has built over the time (still growing at insane rate), which other coins can only dream about. Apparently, bitcoin mining network now exceeds 480000+ petaflops: world's most powerful supercomputers are literally dwarfed compared to this. And it's all about the security: altcoins are looking very fragile on that field. Perhaps only the fact that all of them, even litecoin, are in the deep shadows far from the mainstream medias might be keeping them away from troubles.