I lived on okinawa for 4 yrs and loved georgia coffee. It tastes awesome!!! I think its popular because if is convient being small and in a can easy to carry and most people ride the metro there so carrying a cup of coffee on a crowded train would be difficult so having a can of coffee makes it easier! Also they have machines that have canned hot coffee those are amazing too!!!!
The Canned, prepared coffee market in Japan is huge.
Much of it is the typical, dark roasted (burned), sweetened and milked up (condensed).
All train stations have banks of vending machines. Actually, there are vending machines everywhere.
My personal favorite is : Yes Boss.
Having now admitted to drinking this stuff (much like the Kopi of SE Asia), I must say, it's not a quality product.
Remember, one of Japan"s most popular canned drinks is called Calpis (unfortunately named).