Look! Up there...
"when do we draw the line about what is a casual gamer or not?" ... "Reminder, if the mobile platform does starting running AAA games, do expect the price of those games to match the current price, there is no way a developer will be willing to spend as much money on developing game and then sell it at US$ 0.99"
I think you have answered your own question.
"Casual Gaming" (vs. Living Room/Hardcore/Full Fat gaming, whatever..) is not defined by platform, it is defined by attention span. Casual games are those that can be picked up and put down at will, e.g for five minutes at a time, without the need to invest dozens of hours of concentrated play to get the full experience out of the game.
Hence the £/$0.99 price point; these are the kind of games that can be developed by a small team with a relatively small investment due to the emphasis on 'fun' and 'game-play', vs the £/$35+ 'hardcore' game which requires a distinctly cinematic budget to develop (and test) vast quantities of 'shock and awe' content and/or "depth and complexity" which the casual gamer will not benefit from due to not having the necessary time or inclination to invest the required effort.
The key to success in the casual sphere seems to be getting the 'hook' of the game play mechanics just right, and if you can combine that with some off-kilter visual aesthetics so much the better. Unsurprisingly, the hotbed of innovative low-cost games at the moment seems to be (it was ever thus) the PC! There is a tonne of stuff out there in the £/$5.99 to £/$9.99 bracket that is well worth the money, and I don't just mean last year's failed hits being remaindered/recycled to try and recoup some of their losses (or Farcebook 'social' gaming which is an entirely different type of con).
By comparison to PC indie games, most of the mobile/casual games I have tried or seen seem boring by comparison. There is no particular reason why that should be the case (unfortunate, because you can't fit a PC in your back pocket for when you have five minutes to kill). It just seems that the open/upgradeable nature and relatively low barriers to entry of the PC attracts the most creative (independent) minds, whereas Android/iPhone mobile gaming seems to be drowning in corporately spawned derivative tat chasing the 'mass market'. Maybe developers are put off because it is very hard to get noticed amongst hundreds of thousands of other apps, whereas a stand-out game in the PC arena is competing with one or two orders of magnitude fewer competing games.
On the other hand, consoles are a victim of their own 'success'. If you are a newbie who wants to develop for consoles, forget it, because it's a closed shop requiring SDKs and signing your life away on NDAs, royalty agreements, etc. You need to be a fairly serious game studio with financial backing (in turn requiring a track record) before you can even start. Hardly encourages creative thinking, small projects or talented new entrants, which is why all you'll generally get is (big) teamthink and predictable sequels for the highest price they think they can fleece you for, exactly the same no-risk business model as Hollywood movies. No thanks.