Well, no. You're making a very similar mistake that I think Manny might be making; taking your personal experience and generalizing it
too much. WTF sport Taekwondo is basically kicking, period. When I trained at a WTF-style club in college the instructor, who was a Korean national and an international referee made the point of telling us more than once that in all his years of reffing (which included many international competitions) he'd only seen
six punches scored for points.
But the fact of the matter is that WTF Taekwondo is geared to the Olympics and so many schools just do Olympic style sparring (even those who aren't sending elite atheletes to team trials or WC's which is odd but that's another topic entirely).
Other TKD orgs such as the ITF have international tournaments but their rule set actually encourages hand techniques, not just kicking. It's a matter of recognizing that there is a wider world out there besides the WTF. There are plenty of Kukkiwon certified instructors who would disagree with your statement, too, I think.
And yet, absolutely speaking, it's not necessary since TKD has many hand techniques, including many for close range fighting (and that doesn't include elbow strikes or kicking with the knee, I mean actual punches and strikes with the hand).
Crossing training can be good as long as one already has a firm foundation in their core style, of course, but what you are talking about only demonstrates a shortcoming in the training one receives, not in the style in which they train.
I agree with this sentiment whole heartedly. Conversely, however, it irritates me when people say Taekwon-Do is just kicks!
That's too bad as, from my personal experience, I'd definitely tell them yes. Very effective.
Pax,
Chris