It is a strawman.
I'm not as enamoured of Apple as I once was, but I don't think it has anything to do with the absence of Steve Jobs, I think it has all kinds of things to do with Underdog Apple vs. Dominant Apple. It was always a bit of a shitty corp that made good products and the occasional dud, and lagged the competition in online services (except arguably iTunes), now it's a shitty world-dominating megacorp that makes good products and the occasional dud, and lags the competition in most online services (and I've personally come to really detest iTunes). More than ever, those products and services are aimed at the regular consumer and not the nerdy pro, which unsurprisingly alienates a certain segment of the past, present or potential user base.
But the whole "magic ideas" thing is bunk & bollocks. With and without Jobs, those supposedly "magic" ideas have had four things in common:
1) They were not absolutely novel. All involved a rethinking and refinement of things that were already out there but either hideously expensive (the GUI-based computer), badly designed (the laptop), nerdy/overly complex/niche products (MP3 players, smartphones, small form factor desktop computers), or failed products (tablet computers). This is not magic, it's just smart business. Recognize opportunity, identify flaws in existing products, build something better.
2) They have never come at a furious pace. 1984 (Mac), 1987 (Newton, sans Jobs), 1991 (Powerbook, sans Jobs), 1998 (iMac), 2001 (iPod), 2007 (iPhone), 2010 (iPad). Average gap around three years.
3) They were all poo-poohed by large numbers of pundits, competitors and even Apple fans upon announcement. Every single one of Apple's successful products gets this treatment. Except maybe Powerbook, I don't remember.
4) They all started out relatively modest and earned most of their success through constant iteration, improvement and refinement. Next time you find yourself dismissing the iPhone 5s as just an incremental improvement over the 5, consider how the 5, 4s, 4, 3G were all just incremental improvements over their immediate predecessor. Then compare the 5s to the original iPhone. Arguably, the real genius of Apple is not in the big magical idea, but in the commitment to making a good product out of the gate and then improving it generation after generation.
My opinion: there's no reason Apple can't do it again. There's no guarantee they will, but then again there never was. But it's too soon to declare the beast dead. There's just no solid evidence for it.