Yeah, they should just ignore the enormous iOS base because console players are "faithful." It's always wise to ignore enormous amounts of profit to appease the delicate feelings of fanboys who feel a sense of betrayal at companies developing for other platforms.
It's not quite that simple.
Success on iOS and Android is becoming increasingly challenging, if only due to the sheer amount of competition. Android games are also incredibly easy to pirate, hence the overwhelming amount of f2p titles.
Regardless, a more interesting observation is the relative success of specific genre types and interaction methods across touchscreen devices. For example, in the current top 100 paid iOS apps (of which the vast majority are games) there are only 2 games that could be described as shooters. GTA3 and Vice City. So no FPS games at all, just a pair of games from one of the most successful gaming franchises in history.
So while there's certainly an audience for more hardcore games on these platforms, the "enormous iOS base" is more concerned with games like Kingdom Rush and Plants vs Zombies. While the greatest part of that trend is due to the nature of the audience at large, I.e. causal/non-gamers that make up a large portion of the Clash of Clans player base, there's also an element of suitable interaction methods in that the most successful games on touchscreen devices are built around the input primary method.
The GTA iOS/Android ports are great games, but most reviews made mention of the relative unsuitability of touchscreen controls - and for good reason. The games were designed to be played with control pads that had analogue sticks. Sure, they also work very successfully with a keyboard and mouse due to the cross-compatibility of those peripherals, but and awful lot gets lost in the translation to buttonless touchscreen interfaces. FPS games do not work very well on touchscreen devices. You can play them, and some people are happy to, but the game type is definitely better suited to other platforms.
Deus Ex is primarily a first-person game. The guys in the video announcing the game explained that they have made it as simple to control as possible due to the primary input method being touchscreens. Part of that simplification is a lock on system. Does moving from complete free-aim control to a lock on system detract anything from the experience? I don't know. I'll have to play it before I decide, but already they have had to compromise the established control methodology that exists in the other games in the series. That said, maybe it works perfectly and can provide a similar enough experience for the change to be considered irrelevant.
The last factor is the actual target audience. I don't know whether this game is actually canonical but the narrative picks up after the events of a Deus Ex novel. It seems to me that they are targeting existing fans of the series. I'm sure you'll be able to just pick up this game without having played the previous titles or read the novel and be able to enjoy it on its own, but I suspect that the game would see a higher number of sales on PSN/XBLA or perhaps even Vita. I love the series so I'll take what I can get, but I don't think it's unfair to say that I would much rather experience the game on a different platform - one I consider better suited to the game type that doesn't require any sacrifices to fit.
