Is this stuff LEGAL?

I saw some pretty good emulators out there for free, they're mainly older ones, though. And they're free. Ok, I understand that fairly well. The game ISOs and ROMs are free. Huh? Why would I fish around for a Xbox that's around $500-$600 when I could get emulators and all the ROMs and ISOs I want for FREE? Is there something I'm missing?