I don't think bruce and neil are keeping folks attention or winning new folks over with their new music. Their contemporary releases have received some pretty lukewarm reviews. They're keeping attention by staying active and touring.
bruce seems to have steered clear of the technobabble, neil's foray into breaking new technological ground was that PONO thingamajig - that doesn't seem to have gone over too well. maybe not as bad as the U2+Apple release effort, but i've seen a few news stories portraying Neil as a grumpy old dude.
Point is, they've both made some cool music recently (like U2), but the things keeping those guys 'relevant' and finding new ears in the masses are those classic tunes they're responsible for, not 20 somethings digesting "Wrecking Ball" from front to back (great title track, btw, and a great live song, but the people are packing the stadium for a few other tunes, i imagine).
maybe teenagers and 20-somethings are still discovering the pleasures of "Harvest" and "Born to Run" (and always will) for themselves, and that's sustaining their popularity? the major difference, as i see it, is that they're not talking about winning new people over or maintaining 'relevance' with their new music the way U2 talks about it. They're dignified legacy acts who continue to make music they care about, i reckon, and there's nothing wrong with that. what would U2 need to do to find a groove like that?
Do you really believe Songs of Innocence had any bigger positive effect than, say, Wrecking Ball did?
Are people buying tickets because they're really jonesing to see some acoustic Song for Someone?