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I'm very strongly in favor of getting AGS to output to as many platforms as possible.

The more accessible AGS-made adventure games are, the better.

As for other adventure games on iPhone, try looking at:
-Return to Mysterious Island
-Myst
-Riven (coming soon to iPhone)
-Monkey Island series (1 and 2)
-1112 (multiple episodes)
-Secret of Grisly Manor
-Beneath a Steel Sky

Also, some of Telltale Games' games are available on iPad.