I think that many people are dramatically over-estimating the potential long term growth of the gaming market on phones and tablets ...
The primary reason people buy a cellphone is as a communication device and as a result the majority of people who own these devices with a limited interest in them as gaming devices. Of those who do play videogames on them most are extremely casual gamers who are mostly interested in very simple games. This means that a small portion of smart phone users are looking for games similar to traditional handheld games on these devices. When you consider the multiple form factors (smart phone, small tablet and full sized tablet), the different operating systems (ios, Android, Blackberry, and Windows 8), the multiple generations of hardware 'in the wild' (probably 3 or 4 years of hardware to target), and different capabilities to target different price points ($100 phones for pay as you go to $800 phones for subsidized cellphone plans) the market that does exist is splintered across a pretty diverse series of platforms. Add to all of that the fact that there is (practically) no protection against software theft on these platforms, a market that shows little/no ability to support games that are sold for significantly more than $1 or $5, and that most successful products soon see multiple rip-offs that clone their gameplay to cash in on their success and you start to see a picture that is less damaging to existing handhelds.