How does alcohol keep smell and taste flavors in wine?
First of all, ethanol has its own smell (which we perceive as taste), it also can stimulate pain sensors in the mouth. Therefore alcohol free wine will taste different.

The process of separating alcohol from wine is quite invasive: the water/alcohol is separated from flavour and colour compounds by reverse osmosis, then the water is distilled to remove alcohol, the water is added back, to the concentrated wine flavour. This process is surprisingly good at not removing anything but the alcohol, but it does change the flavour. Other small light volatile compounds are lost by this process. Tannins are also lost in this process, resulting in reds that lack body

Next the presence of alcohol helps some aroma compounds to evaporate. This means that the aroma of the wine changes. The scent chemicals can't get into the air without alcohol to carry them. 

Finally, of course, the best wine is sold with alcohol. When you drink non-alcoholic wine, you are usually drinking a lower quality source wine.

source: http://winefolly.com/tutorial/non-alcoholic-wine/