The US especially tends to produce varietals as opposed to meritage blends, though we're finally starting to blend our grapes as well. You still can buy a straight varietal based on where its grown though- for instance, there are about 12 different major Zinfandel regions of California and all of them have different characteristics in the flavors of the grape- I personally have a preference for Paso Robles over the others, but that's just me. The soil still matters- that's why people travel to Napa to go on a vineyard crawl.
The best way to learn the difference is to drink and to read (and talking to someone who knows the differences!). Over time you'll realize that the land, the year and who made it matter just as much as the grapes themselves that went into it.
And yes, we're blending some here now- for instance, Opus One is a blend- and a very tasty one at that. It's a bordeaux style blend, but tastes different since it's all Oakville grapes instead of French- no less delicious though