"To answer the part of your question that hasn't been addressed ("Why do I even need to do this at all? Why doesn't it just use all available features by default?"): Backwards compatibility."

It has been addressed, it's discussed in feature linked to in first reply, and expanded upon in others.

In reply to Re^2: Why do I need 'use 5.010;' ahen I am running '5.24' by marto
in thread Why do I need 'use 5.010;' ahen I am running '5.24' by jason.jackal

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