Actually there are many unicyclists who do commute via unicycle. Think about it:
A unicycle is highly maneuverable. Busy sidewalks or even streets (legal definition is sometimes fuzzy, as with segway) are not a problem.
A unicycle can fit pretty much anywhere, and due to its weight can be carried or pushed easily if you are out of "oomph"
A unicycle is a form of personal expression. It says "I am willing to put the time into something that other people would just give up on".
A unicycle is healthy. On a segway or bike, you have motors or different gears to help you out (All right, maybe a dozen unicycles in the world are exceptions such as blue shift (two internal gears), a couple motorized unis, the uber coker I referred to earlier) Your leg muscles, balance, coordination and general terrain awareness are improved.
You can go a lot farther than 17 miles on a unicycle, especially up on back roads. And you can easily carry your power supply.
A unicycle is very versatile. Have you ever seen someone wheel walk (move while balanced and pushing wheel with feet) a segway? How about jump onto a picnic table? And how many segway owners can ride off a several foot drop and still own a rideable segway? These are street and trials tricks you could conceivably do on the way to work.
A unicycle is a good way to get to know your friends better. Because your friends will want to ride it, and it takes time and hard work to learn. Time and hard work strengthen friendships. You would certainly let a friend ride a segway, but really anyone who can walk can ride a segway, so there would not be that bonding time.
Lastly, a good learning unicycle is affordable. Maybe $80-$90, and you really don't have to upgrade. For a better one you can spend about $200, for the best (which are insanely durable) $500-$1000
I'll probably be commuting to school next year on unicycle. I couldn't do it this year because I had to drive our exchange student to school too.