Apple has an advantage for sure - it's a circa $700 universal platform with a wealth of other applications and accessories to go with it.
The Garmin 796 is $2,500 and essentially both products are *capable* of the same functions - only limited by the imagination of the programmers such as the OZRunways guys.
Both are non-TSO'ed and are likely to never be, so there's no point factoring that into the equation
There is a massive market for the iPad that is almost untapped except for some foreign companies for Analogue to Digital converters so that the iPad can become an MFD like the Avidyne and Garmin 1000's. The potential is only limited by the imagination of the programmer and the processing power of the iPad.