They aren't, as earning the penalty has no connection to being the person who takes it. You're confusing the measuring of two different things.
Completely disagree. If a player is fouled in the opposition box, they are statistically likely to be an attacking player (though of course, I know this isn't the case
every time) so there is certainly an increased chance that said player is the striker.
For argument's sake, I decided to look at this thread's most recently discussed player, Saido Berahino.
Last season, he scored four penalties in the league, which can be summarised like this:
16/8/14 – Penalty against Sunderland (42’) earned by Anichebe
4/10/14 – Penalty against Liverpool (56’) earned by
Berahino
25/10/14 – Penalty against Palace (90+3’) earned by Anichebe
18/05/15 – Penalty against Chelsea (47’) earned by
Berahino
All four of these penalties were conceded by fouling West Brom's attacking players, and half of them via fouls upon Berahino himself. So yeah, I'd say he's at least
somewhat responsible for those goals scored, even when ignoring the composure, etc, required to put them away.
And your whole point ignores the propensity of players (particularly attackers) to wish to take penalties they've 'earned'. Even so far as grabbing the ball off of their teammates.