See answer from @gaige in comments, who said:-
I ran a quick test on this by removing the "T" from the string and it captured the correct date. Unless you know you're getting an ISO format date in a block of text (as opposed to some formatted data), you are probably OK. For formatted data where you know you're getting a date, I'd suggest Peter Hosey's ISO 8601 NSDateFormatter as an excellent parsing choice.
Thanks.