How much longer is this going to be true, if gamers also buy mobile devices? If nothing else, the money they spent elsewhere may reduce the money they would spend on core gaming.
In a lot of ways, digital convergence has made the "good enough" principle true. Lossy compression for music is "good enough" for music playback as it allows people to carry a lot of music on tiny devices.
Cell phone cameras are "good enough" for a lot of people, especially those who share photos on Flickr and Facebook.
Can mobile gaming be "good enough" even for a lot of core gamers? If core gamers get into these little quirky games during the day, will they still have as much need for core games after work?
The functions which you list all make sense for a portable device.
Music you can listen to while doing multiple other tasks. It's the reason the walkman was so successful. Having the your entire music library to choose from is obviously an advantage over taking a bunch of discs with you (portability for the function while doing other tasks).
The ability to take a picture anywhere at anytime because you will always have your phone on you is again, added function which doesn't negate ones portability by forcing another device to tag along on the go.
Smartphone gaming also makes sense as a "good enough" experience to replace a portable console.
Suggesting portable gaming would supplant console gaming is akin to suggesting a portable exclusive version netflix will dethrone the netflix we know today. People want to watch movies on the bigscreen. This doesn't mean they DON'T want to watch them (or tv shows) on the go, but the primary usage of that entertainment medium is the livingroom bigscreen.
Different use cases.
Or suggesting smartphones will replace DSLR's for professionals.
(or movie studios replacing their cameras with iphones)
Different use case.
Or suggesting professional recording studios will record straight to 128k mp3s.
Different use.
The portability and functionality of smartphones and the like are nice, but they have their place. Including components which replicate other experiences is fine, until those components jeopardize the portability of the device which negates it's primary purpose.
Even assuming technology always progresses and things get better, there are things which will always be limited by the form and function of a portable device which itself is an advantage in keeping the device with you all the time.
It will never replace a professional class camera.
It will never be used to record professional class audio.
It will never be used to record professional class video.
It will never replace the movie watching experience at home.
and it will never replace a console/stb (stationary connected entertainment device).
The things which make it portable, also make it weak in specific areas.
Screen size
Optics
Energy available for processing
Size available for processing
Ergonomics
Those things will never change for a portable device. They will always be a disadvantage to DEDICATED devices.