I'm under 50, but when Jim first posted the link I couldn't get into the page for some reason and didn't want to take a shot at a comment until I'd read the piece.
Now that I have, I think I find myself in agreement with those who commented on the original blog post: there may not be a "this generation's Led Zeppelin" because the underlying environment has changed. It would be somewhat like asking people in the 1970's who would be "this generation's Frank Sinatra." (Arguably, it was, well, Frank Sinatra.)
On the other hand, it was Paul Simon who sang, "Every generation throws a hero up the pop charts" ("Boy in the Bubble") and maybe he's right, although the pop charts are a lot different in my opinion than when Casey Kasem was countin' 'em down.
Even so, I have to question whether "under 50" is the right demographic for the proper answer to this question-- maybe it's more like "under 25"? Maybe I should disqualify myself. The music I tend to listen to is often as old now, or older, than the music my father listened to when I was a child. Example: A 45 in the family cabinet was Sinatra's "Witchcraft" which charted in 1958. A couple of nights ago I watched the video for Blondie's "Rapture" which is now approaching 30 years of age as it hit #1 in 1981.
As for American Idol... I've never been a viewer but my iTunes does have some product from a few of its contestants. AI probably owes more than it admits to "The Original Amateur Hour" although it certainly uses a lot more wattage.