One really should consider running the recommended premium fuel. One problem that has developed with many high compression, direct injection engines is LSPI (Low Speed Pre Ignition). Especaily so in turbo models. It is one of the reasons that dexos1 Gen 2 oil was developed, why the current API spec is SN+, and why ILSAC GF-6 is due out this next spring. All in an attempt to help mitigate LSPI. The ECM can dial back the timing also to try and prevent it, but that does not always do the trick. The only way to mitigate the problem is to run a higher octane fuel.
LSPI is similar to knock, but on a micro level that the vehicle owner may not be able to detect. You won't know there is a problem till the damage is done to pistons, valves, and injectors.
LSPI can be very detrimental to the internals of a engine. It doesn't make much sense to cheap out in this regard. The dealers and such may make the comment that regular is fine to use, but they are interested in selling vehicles. If folks knew they should use premium they might be less inclined to buy the vehicle. The dealer benefits from the sale and the repairs that come later when the results manifest from using an inferior fuel.