Nintendo's hand-holding feature for New Super Mario Bros. Wii, dubbed "demo play," may not be as forgiving as we'd originally thought. One official description of the helpful option throttles back the level-clearing capabilities of demo play.
The Nintendo of Europe product page for New Super Mario Bros. Wii, spotted by Siliconera, says the "dynamic help system" will allow players to "access a mode showing how a level can be completed if you are stuck," which sounds more like helpful tutorial and less like you're outsourcing platforming skill to the Wii.
That description sounds a bit different from the way Shigeru Miyamoto pitched it to USA Today, saying "if a player is experiencing an area of difficulty, this will allow them to clear troubled areas and take over when they're ready."
Going back to the NOE version, it adds that "the best thing about this mode is that you are free to jump into the action you're watching on screen at any time!" Which, err... sounds a lot more like what Miyamoto said in the first place.
Maybe the European product page's description had some specific details lost in translation and we're splitting hairs. My personal hope is that the automatically playing version is the accurate one and that Nintendo of America will get back to us with clarification soon.