Hompy:
Your premise is not necessarily correct. If one were to observe the request for tender for the larger oil companies in the North Sea (UK, Norway etc), one would see that newer aircraft meeting the latest certification standards are being preferred for contract renewal - even though they are more expensive to contract.
The main driver for this change is the calculated cost of the life of an oil company employee; if it can be established that the additional contract cost will be less than the (probable) loss of life due to the lower certification standard, the decision is made (I might add a really difficult and complicated calculation that has to take into account the consequence of each and every improvement between the certification standard of an existing helicopter and that of the proposed).
That this is not true for all oil companies is left for you to ponder.
For scheduled airlines, there is a significant benefit in operating the latest more efficient aircraft as their costs are more related to operation than capital expenditure.