A "trained" ear is indeed, a wonderful gift, but not everyone so blessed. Learning to play any instrument requires a mastery of certain basic's INCLUDING (but not exclusivly)reading music, and knowing basic theory. It's like knowing the alphabet before reading a book. It's basic. It's fundamental, and it's VERY neccissary.
It's great when a player learns how to rely on "listening" but the basics need to be learned first, or any future advancement will be hampered. I rarely read on the job, but I studied my butt off all through high school and college, and those countless hours of training gave me the arsenal I needed to make music.... my "REAL" job. http://members.aol.com/unclemusic/
I encourage ALL players to read. It's really, VERY important. "Playing by ear" comes naturally, and can't really be taught, so it's a good idea to get the "mechanics" down first ... and THEN experiment with your tools. It's alot like singing - it can't be taught. You either have it .... or you don't. A vocal coach can teach you breathing, diction and phrasing tips, but no one can "teach" you how to sing if you don't have the natural tool in the first place.
Study the art, practice the craft, and enjoy the results! It's ALL good. It really is.