People won't be able to sell their work if it's exported as Flash.
True, most people won't want to sell their work, but we're talking about a Commercial version of Construct here, so it should be taken into consideration.
The Mac market is obviously a lot smaller than the PC market, but it's a market none-the-less, and some might like to sell to it.
The Android platform already has a good following, and from various articles I've read over the past couple of months, it's current momentum has exceeded even Google's expectations (and who wouldn't put a few quid on Google to make it a success).
So I'm sure it's going to be just as big a player as the iPhone.
No need to say anything about the iPhone's share of the market, but as with anything Apple, you'll need to make sure you don't sell your soul when you decide to publish on the App Store.
So, for me, they are the important ones, and in the following order:
For me, Flash wouldn't be an incentive to buy Construct 2 (but then, I'm currently beta testing Stencyl