Josey,
BA are indeed being generous. All BA tickets are supplied in an envelope which carries the following statement:
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Notice of baggage liability limitations.
Liability for loss, delay, or damage to baggage is limited unless a higher value is declared in advance and additional charges are paid.
For most international travel the liability limit is approximately US$20 for checked baggage and US$400 per passenger for unchecked baggage.
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No-one said it was fair but the information was presented to you before your flight and it was your decision to carry the valuable baggage you did without informing BA and paying the higher premium.