This strongly suggests they had checked in luggage and simply didn't want to pay even more just to bring some in the cabin. A flight is not like a taxi ride, you're all but guaranteed you need luggage. So I think the cause-effect relationship works the other way. People don't bring hand luggage because they plan based on the cheap fare only to discover it doesn't include that.
The only reason prices are advertised as such is that they can initially stand out as being cheap. Many people will just go for it because it's hard to make an apples to apples comparison with an airline that gives you everything in a single package. Services that are now in a race to the bottom (airlines, mobile operators, etc.) are using these strategies more and more to differentiate themselves. But it's all done through misleading advertisement.
I didn't stalk people about it or anything. I myself actually paid for a bag in order to be able to carry-on my guitar, only to be told at the gate that I needed to gate check it (but with assurances that they'd be very careful, etc - although it's a carbon fiber guitar in a hard case, so I wasn't too worried).
So I got on the plane without a carry-on. Then I noticed... that most other people did too.
The luggage carousel in Berlin was pretty packed, but it's hard to really say how many people did or didn't check. I imagine Ryanair keeps tabs on these things fairly tightly, as its a crucial part of their model.
This strongly suggests they had checked in luggage and simply didn't want to pay even more just to bring some in the cabin. A flight is not like a taxi ride, you're all but guaranteed you need luggage. So I think the cause-effect relationship works the other way. People don't bring hand luggage because they plan based on the cheap fare only to discover it doesn't include that.
The only reason prices are advertised as such is that they can initially stand out as being cheap. Many people will just go for it because it's hard to make an apples to apples comparison with an airline that gives you everything in a single package. Services that are now in a race to the bottom (airlines, mobile operators, etc.) are using these strategies more and more to differentiate themselves. But it's all done through misleading advertisement.