Yes, it is possible but not easy - look at for example Shenandaoh's Desert Fox / Battle of The Bulge). But I don't know if that is a long term model for success. $19.99 is the highest price point you can set for a game and then you are competing with things like FMC2015 or Xcom (heck, you can get GTA San andreas for $6 or so - is your game better than GTA?!?) which are full PC ports. Clever developers will I think make a game for more established platforms, and if successful port to iPad for additional revenue. The iPad has millions of active premium gamers, but a tiny number compared to any non-portable system.
Fact is all iOS categories and ratings are useless to me, mostly rubbish game built for freemium and with loads of marketing wind behind get visibility on the store, while real games get buried and I've had to follow third party website just to even know their existence
At this point App Stores are nothing more than extremely expensive anti viruses for all the applications installed. We'll see on the long term if giving up so much control is worth it for a security scan :|
anyway, even steam has given up, but at least they added curators before opening the early access floodgates