From a technical standpoint, surely the servers running Lambda have an OS and require maintenance internally by Amazon at some level (even if it's dev-ops-abstracted away for their operators). It's just their responsibility instead of yours, and it's also their responsibility to find other work for those servers when your code isn't running (or bear the cost of an idle server). It's like if they were letting you push PHP functions to their web server, using the quoted comparison.
Useful from a business standpoint, yes. Revolutionary, maybe not as much as it seems at first glance. That's the takeaway I got.