S Stock moquette renewal

The moquette used was very poor quality compared to the traditional Underground material.

Do procurement people ever consider the medium/long term implications of buying cheap?

In at least some cases they do. However, the decision on what to purchase is a combination of upfront cost, expected life and budget available at the time of purchase. In some cases the extent to which the various factors can be considered are limited (intentionally or otherwise) by procurement rules.
For example, Product A is half the price of Product B but is expected to last only one third as long. In the abstract you would expect any sensible decision maker to purchase Product B, however they may only have the budget for Product A. Alternatively and/or additionally, if purchasing the more expensive product requires writing an extensive justification of the decision but purchasing the cheaper product does not this creates a disincentive to choosing the option with better long-term value, particularly if the person/team responsible for writing the justification is overworked. These effects are magnified if the expected life of both products is longer than the current budgetary period, increasing roughly proportionally with the difference between the two (e.g. 20 years is a lot longer ahead when working to 5 year budgets than to 10 year budgets)

Seats were recovered on HO at Acton works every 5-6 years