I'll bite. Explaining to a "geek with low reading comprehension", what is the actual benefit to the iPhone being 64-bit?
There is also a new instruction set to go along with the bump to 64-bits which improves things. However, I remember Herb Sutter saying that, in the case of x64, Microsoft generally found that the improved instruction set performance gains were a wash due to the increased cache misses caused by the doubling of the pointer width. I'm not sure how much ARM 64-bit instruction set improves things.
Yeah, I don't think they ever supported GC in iOS. Now that you mention it, it's probably not a coincidence that it was added to the Mac shortly after the entire product line had switched to 64-bit. You could still do it in 32-bit, but I doubt they were expecting many developers to start writing new 32-bit apps at that point.
What does use a conservative garbage collector on iOS, however, is Safari's JS engine. But I assume that the conservative scan is only used on the stack (that's what FF does), since it would be kind of silly to do a conservative scan of the heap for a language that doesn't support pointers. So it doesn't seem likely under normal circumstances that you'd have many false hits even with 32-bits.