Given that so many bartenders and waiters call anything served in a flute-shaped glass "Champagne," it's no wonder people think Prosecco is Champagne. Unfortunately, the two are vastly different despite the fact that they're both bubbly.
First, Champagne is really a subset of sparkling wine and by French law must be made in the Champagne region to merit the label—and with any combination of these three grapes: Chardonnay, Pinot Noir, and Pinot Meunier. Everything else in this world, no matter how good or bad, is just sparkling wine (though it may also have a special designation like Proseccco, which signifies that it was made in Italy and uses Glera grapes).
Second, Champagne is made in a very unique—and labor-intensive—way. All sparkling wines go through two fermentations; the first to turn grape juice into wine, and the second to give the wine bubbles. It's that second process that makes a world of difference. Champagne producers—and anyone who uses the "Traditional Method"—take great pains to execute that second fermentation in the bottle, which is a colossal pain in the neck, because when that fermentation ends, you have to separate the lees (solids leftover from fermentation) from the wine, without losing the bubbles that have been trapped in the bottle as a result of that second fermentation. This is why these wines cost so much money: the slower and more painstaking the winemaking process, the more complex—and expensive—the result.
A simpler method, called the Charmat process, works in such a way that the second fermentation occurs in large tanks and is produced quickly—as opposed to over several years. Prosecco is made in the Charmat method.
Apart from region, grape, and price, the greatest difference between these two styles is taste: Traditional Method sparklers possess complex, toasty, biscuity aromas and flavors, while tank-made sparklers pack more fresh fruit aromas and flavors. You get what you pay for, but sometimes a glass of Prosecco that tastes like just-picked peaches and apricots is exactly what you're looking for at a fraction of the cost.
So my final answer is: No, Prosecco is not merely the poor man's Champagne, though it is usually less expensive than the French stuff.
—Follow Anthony Giglio on Twitter at @WineWiseGuy.
• • •