Yes, storage and virtualisation, as was said, but that sounds less different than it actually is. It feels more like a mini vs mainframe difference. AIX is vastly larger in that respect on AIX 7 than on AIX 5L, for example. IBM seems to have invested a lot of effort into making AIX huge in VM, clustering, storage, and more . AIX 7 is much more into this than e.g. AIX 5L.

As for standard Unix tools - or rather "Linux" or OSS tools these days - they are not that difficult to find and are for the most part readily available. IBM used to supply a lot of that directly, but these can be found elsewhere and for myself I work on AIX more or less as I would on Linux.

When that's said, if you don't actually need the AIX-specific features you can as well run Linux. But if what that site indicates is correct then I'm a bit surprised - IBM seems to have invested a lot in those "differences" the last couple of decades and it's strange if they're abandoning that, or planning to - yes, you can run Linux on IBM hardware, but then.. why? Sounds to me they'll lose HW sales if they abandon AIX. Their strategy has been to make the system more and more Linux-like in many ways (compiler has gcc-compatible options, as one example), but at the same time add large-scale features which Linux doesn't have. Which is clearly why AIX has survived while none of the others have (IRIX, Solaris, Tru64..) - those Unix systems didn't really bring anything more than a Linux system could. AIX does.