Actually the Caps Lock is a much older relic. It was on nearly every manual typewriter, long before the IBM Selectric or the IBM PC keyboard. It worked by engaging a hook on the shift key, holding it down. On manual typewriters, holding down the shift key took muscle power, since you were holding up the whole weight of the platen (the roller), so having a caps lock wasn't just a convenience that reduced awkwardness, it actually relieved the stress on the finger.
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Actually the Caps Lock is a much older relic. It was on nearly every manual typewriter, long before the IBM Selectric or the IBM PC keyboard. It worked by engaging a hook on the shift key, holding it down. On manual typewriters, holding down the shift key took muscle power, since you were holding up the whole weight of the platen (the roller), so having a caps lock wasn't just a convenience that reduced awkwardness, it actually relieved the stress on the finger.