The problem with the Zune is the lack of accessories.
For instance I own a Zune. I bought a nice Kenwood 7" DVD/Nav system for my car, it also includes a USB port for plugging in an iPod (and offers full intergration) or any generic USB storage device... sadly the Zune is not supported.
HOWEVER there is a headphone looking input on the front that not only supports audio but video as well... the Zune has a similar A/V port on it, if I had a cable to connect these two I could get the Zune audio and Video output in my car... but alas such a cable does not exist (believe me, I've looked everywhere).
Sure MS sells an "av kit" that converts the 3.5mm jack to RCA outputs but they charge $30 for it and I'd still need to convert from RCA back to 3.5mm to plug it into my car stereo. I'm not about to spend $60+ for a rats nest of wires and adapters in my car when a 6" straight through cable would do just fine... and SHOULD cost pennies for them to make and well less than $5 for me to buy.
MS isn't making any accessories worth buying really, and they're not really encouraging anyone to support their product either... if they really wanted to take over apple the real battle is in the Accessory market. Opening the port standard would open the flood gates for thousands of cheap accessories, if they still want to make a profit they can offer some kind of certification process for companies to place an "official zune product" logo on their accessory...
MS needs to realize that being stingy doesn't always make the most money in the long run...