Usually the more sophisticated oil change indicators measure the way you drive and adjust for that - ie, if you're doing a lot of freeway miles you're probably getting longer intervals as that's not as hard on the oil as lots of stop and go in town. They are however making the assumption that you are using an oil that meets all the manufacturer's specification regarding viscosity, API grade and other specs. Oh, and the part that's most likely to be overlooked - an OEM or OEM quality (or better) oil filter. If you don't have the latter, you probably have to change the oil more often because of the diminished filtration quality of the oil filter. There's no point in using good oil with a good additive package that keeps the contaminants in suspension if they'll just pass through the oil filter or the oil filter's bypass valve because the filter isn't doing its job.
So, for OEM quality or better filters and OEM quality or better oil, follow the oil change indicator light, or if you really want to geek out, get an oil analysis done to determine how often you need to change the oil.
That said, the one hour oil change tech isn't wrong by suggesting 3k intervals in the sense that you won't hurt the car if you use a good oil; the only pain you'll feel is going to be in your wallet. Asking them if you need to change the oil more often than the manufacturer's recommendations is a bit like asking at McD if you should add a second cheese burger to your order.
The 3k interval certainly made sense a couple of decades ago, but the quality of the oils and the filtration has improved massively since (again, for good quality oils), as have the manufacturing tolerances for engines. So basically now you have oils that don't break down as quickly as they used to and you've got engines that are machined to tighter tolerances and thus have less contaminants pass into the oil so you don't need to change the oil quite as often as you used to.
However, if you use the cheapest oil available with the cheapest oil filter, then you should change your oil more often, or just buy better quality parts.