A non-issue for us. I'm not a big fan of the reusable mugs either way. Mind, we own a bunch of them.
I'd venture to say, the handles made them bulky to ship to WDW from the company that makes them. WDW will probably pay lower shipping costs.
Funny thing is, it takes up the same exact amount of space. I believe they are still using Whirly mugs, and comparing these two styles (which I believe are accurate to the types in question) http://www.whirleydrinkworks.com/productinfo.php?prod-code=CM-16&cat=jw&sub=c and http://www.whirleydrinkworks.com/productinfo.php?prod-code=CM-16H&cat=jw&sub=c, both take the same exact amount of space to pack 75 in a shipper. (Click the details tab on the link) The only difference between the two is a slight bit of weight. And since they are dealing in pallets of mugs at once, potentially filling an entire truck, I'm not sure if there is any real cost savings on weight. At that volume they may just be charged on flat rate for the whole filled truck.
You can do that? I never thought that was possible.
Hacksaws are a wonderful thing.....