Actually the only reason you saw Samus' final smash get that OHKO is because:
1. That comp was on "ridiculously easy" (no, not really, but it might as well have been)
2. It was point blank, which any decent player shouldn't let happen
3. He waited, like, a year to fire the shot by then a human would have stolen it from him and used it his/herself.
4. Due to number 1, comp didn't Up+B recovery.
Also...Pit's final smash looks sooo lackluster. It's too slow to really do any killing if everyone is ready for it. Then again, chances are nobody will be ready for it as he can activate it right after everyone's scrambled for the smash ball.