You may be right that it's been run past a seller group, but I still very much struggle to believe this.
However, as far as cost is concerned, I'm sorry, but you are miles out!
The only cost for something like this is storage cost.
There is no ongoing other cost at all to display something.
Now whether or not something like this is displayed on a listing is actually immaterial, as Ebay will still store that information. Which in turn means that there is no cost saving by not displaying it.
So the only possible "cost", is the speed of service and frankly, unless this information is held on a server in Timbuktu, there is very little difference in the speed of showing the page to the customer.
As to actually making the change, I would be willing to bet that it takes a few minutes by someone familiar with the code. Some testing, then a little longer to compile it and deploy it overnight.
Whilst they may make some changes in the way that you describe, to do so is a very short-sighted view for any large company. Of all the big companies I have worked at, I have never seen changes made with the hope that nobody notices! They are generally made with a view to improving things and not just saving money.
Oh and by the way, big companies like this who have finance dept's, usually get the signoff from the finance dept prior to any work commencing and it extremely rare that it works the other way around.
The only time that kind of thing happens, is generally in emergency situations.
