The classic "Smart Phone, stupid user". Roaming is there in black and white on the contract, and detailed in "dumbed down" language on all the main mobile networks websites. All Smartphones have full manual on them, and help functions - and all can have data roaming turned off. Ignorance is no excuse IMHO, and neither is the "but it's a rip off" line. People know the cost of data abroad (see above RE: contract), the know how to turn it of (see above RE: phones) yet are still amazed when they get billed.
Edit: sorry, wasnt called SOG "stupid", came out a bit wrong.