Well, not everyone runs out and buys every single model of iphone that comes out so stop associating anyone that buys a new iphone as an Apple Fanboy. If you don't already own an iphone and buying one, with the above kinda thinking, that would be like saying why buy an iphone 8 or X or even a 7 when you can get an 5SE for a lot less and it answers calls just the same.
OP, both pistols are fantastic shooters. There are slight ergonomic differences that I would suggest physically testing both out before making a decision.
For me, I preferred the feel of the aluminum grips, slightly higher undercut by the beaver tail and trigger guard, the more aggressive frontstrap/backstrap checkering, competition hammer, added front weight, shorter trigger reset, oversize mag release and the aggressive slide serrations plus the non-visible features during manufacturing that Slavex pointed out in a previous thread. Upgrading a Shadow to how "I" would like it with a competition hammer, less curved trigger, disconnector, oversized mag release and grip panels alone would set me back another $400.+ easily and that puts the cost right up there with an S2 and I still don't get the ergonomics and features of the S2 receiver. Hence why the S2 was a no-brainer to me.
The S1 guys above did bring up a very important point. The S2's heavier weight will mean that you can't shoot IDPA so... buy both! lol