The lack of tannins, malolactic fermentation, and often the lack of oak will make it pretty obvious they are different. It's like saying you can't taste the difference between a Guiness and a Bud, because you've never had them before? Maybe you don't know which is which with a blindfold on, but you can taste the difference.
My point is mostly about the $3-10 wines which have pretty simple notes. They have very particular styles and relatively restricted grape varietals due to cost, availability, and customer expectations. I'm sure for the right money a good winemaker could take the right white grape and make it taste like a cheap red without the color (lots of skin contact, malolactic fermentation, heavy oak, and some age. On the other spectrum, I'm sure you could screw up and make any wine/grape so terrible you couldn't tell what it came from.
There are also people who couldn't tell the difference between a pilsner and an ale, I suppose.