If you're a CEO/Executive and you use your competitor's products, you'll be in good shape to know their strengths and weaknesses. On the other hand, if you're like Steve Ballmer, you'll refer to your competition as "Cancer" and ban the use of all competitor's products. Then you'll never ever know that your products are 10 years behind, since you've intentionally prevented yourself from knowing that.
I think that "admits" in an odd word in the headline. I would be very, very worried if he didn't use Apple products.
Citations of Ballmer insanity:
http://www.theregister.co.uk/2001/06/02/ballmer_linux_is_a_c...