These are always questionable metrics
I am not sure why anyone is surprised to see EMC leading any chart that has to do with storage revenues. There systems are ALWAYS more expensive then similarly configured systems from competitors (HDS might be the exception, and with good reason), and they are the least efficient systems out there, meaning you will need more physical storage space than competitors since they require the most disk/flash for whatever you are going to load up on their systems, so of course they ship more raw disk than anyone else. This is on top of them being the largest storage vendor in the world for other dubious reasons.
That said - who really cares about AFA's? What percentage of companies out there really uses or needs them in the first place?
NetApp recently started publishing storage limits to FAS boxes with SSDs in them since some of their customers configured them and bought them as AFAs anyway. This was probably also done to shut up anyone whining about them not having an all flash array.
It is a small portion of their customer base, because few companies require AFAs for their business, and those that do don't need it for everything.
EMCs flash caching solutions are notoriously bad and difficult to configure, and they are all about shaking more money out of customers, so it makes sense for them to push their current customers into AFAs for specific purposes (reporting databases, highly transaction stuff, etc). Not that these wouldn't perform well on a hybrid system from another vendor, its just that EMC doesn't have a good hybrid system and they are already in the position of having locked in customers that buy whatever they tell them to buy, so its an easy sale.