I have a lot of sympathy for dealers when it comes to computerised gizmos (and the converse as well, depending on whether they did what they are meant to do or not).
When I was dealing with dealers (regarding diagnostic issues) they were being paid a standard repair rate for warranty - the jobs are costed based on a standard repair time, and sometimes only paid if the equipment is proven faulty when it arrives back at the supplier.
With the complexity of cars growing faster than the diagnostic capability it's often nearly impossible for the dealer to find out which parts need changing - so some will start changing parts based on guesswork. If things go well they get good advice from technical support folks, but in some cases those giving the advice don't know what they are saying. In other cases the dealer gets it wrong by not asking for advice or not following it properly.
In the really tough cases there is a software bug so it doesn't matter what gets replaced by the dealer, as the software is still at fault (e.g. the supplier may not be aware of the issue or not been able to release an update).
So dealers may spend an immense amount of time trying to diagnose an odd fault, with no success. When they start changing parts by guesswork they can be out of pocket very quickly. In other cases there may be an issue but 'big brother' has decided to save costs and not allow dealers to do repairs if it's not safety critical. I've yet to see a waranty repair where the dealer makes something out of it.
Fortunately in my experience most issues are looked at carefully with the aim of finding the route cause and rectifying it. Finding the route cause is sometimes trickier than others - especially if the customer or dealer gives misleading failure symptoms (you'd be amazed how different a real fault can be, compared to what a customer/driver/dealer thought had happened).
In 99% of cases the dealer is just a middle man as they can only work with what they're given. The vehicle diagnostics has to work well, and that was the end product of many things that happened years before the first car gets down a production line. When faults occur and the diagnostics don't find the issue, it's then down to the dealer network to make sure the right people are informed, and then the vehicle engineering and supplier technical guys to find out what's actually going on (how many cars affected and what are the symptoms). The dealers job is only to make sure the problem car is around when people want to check something (e.g. by offering a temporary replacement) - but for intermittent problems it can be like trying to find a needle in a haystack.

Sorry - got transported back in time by a few years then

it was good fun dealing with new technology releases at the time - but I'm especially glad to have left that all behind!
Ray. MMOC#47368. Forum moderator.
Jan 06: The Minor SII Africa adventure:
http://www.minor-detour.com
Oct 06: back from Dresden with my Trabant 601 Kombi
Jan 07: back from a month thru North Africa (via Timbuktu) in a S3 Landy
June 07 - back from Zwickau Trabi Treffen
Aug 07 & Aug 08 - back from the Lands End to Orkney in 71 pickup
Sept 2010 - finally gave up breaking down in a SII Landy...
where to break down next?
2013... managed to seize my 1275 just by driving it round the block
